Hi, and welcome to the forums...I'm sorry, that really does look suspect, very much like Yellow Fungus to me. I want to see what the opinions of others are, but in my experience that looks a lot like Yellow Fungus, it usually appears as spots or patches that are yellow in color, but they are also very rough and almost scabby, which is what usually differentiates the look of Yellow Fungus from other more benign conditions like retained shed. The only way to know for sure is to get him to an experienced reptile vet for a skin scraping test, which you absolutely are going to have to do. I know you said you're broke until this Friday, but I would find the closest certified reptile vet or at the very least an experienced reptile specialist vet to you right now and make an appointment for Friday now. The reason this is so urgent is that Yellow Fungus is extremely difficult to treat and even harder to totally cure, but it can be done IF IT'S DIAGNOSED EARLY AND PROPER TREATMENT IS STARTED EARLY! THIS IS CRUCIAL FOR HIM TO HAVE ANY CHANCE OF SURVIVING THIS AND IT BEING CURED. A skin scraping test shouldn't cost too much, and the test itself can be done by an "exotics" vet, but I cannot stress enough that if the test comes back positive and he does in fact have Yellow Fungus, you need a reptile specialist vet that is very experienced and familiar with both Yellow Fungus and Bearded Dragons. "Exotics" vets tend to only make things much, much worse...
In the meantime, stop all baths, no more baths at all until you know what this is for sure, as moisture causes most all fungal infections to grow and spread. You can still dilute the Betadine or Hibiclens, which in my opinion is much more effective than the iodine, as Hibiclens is now used in scrub packs that surgeons use to scrub-in to surgeries with because it kill EVERYTHING including most all fungi and viruses, in warm water and then use sterile gauze or sterile cotton swabs to apply this antiseptic to only the spots themselves, but you do not want to actually submerge him in the water/Betadine solution, as it may very well cause the fungus to spread everywhere. After you cleanse each spot with the antiseptic, pat him dry very, very well, and then apply a small amount of Lamisil to each spot, being sure to rub it in fully. I would do this process twice a day. This will not at all cure this if it is Yellow Fungus, but it can help slow down the external spreading of the infection. You also need to completely disinfect his entire tank, both inside and out, and everything inside and on top of his tank, all the decor and bowls, the light fixtures, the lid, everything, in either F10 disinfectant or bleach and very, very hot water, then rinse everything very well until all odors of the bleach or the F10 is gone, dry it thoroughly with clean paper towels, and then use only clean, dry paper towels in the bottom of the tank as the substrate, being sure to throw them away as soon as they're soiled, and then replace all of them daily. I would wash your hands with antibacterial soap or Hibiclens scrub before handling him and his tank/decor/food, then also afterwards, and wearing gloves while doing it in addition to washing your hands is a good idea as well.
I'm very sorry this happened to you, you were only trying to give a loving home to a beardie who obviously had a prior owner that didn't care one bit about him. He no doubt put him up for sale (Craigslist?) because he was well aware that he had Yellow Fungus or something similar and did not care enough about the poor little guy to help him. That's exactly why he's disappeared. He is hopefully feeling enormous guilt, I would be emailing or texting him every single day, telling him that this poor little guy has a potentially lethal disease. He deserves to be shamed...
I don't know how much you know about Yellow Fungus, but it is highly contagious, so if you have any other reptiles or amphibians you need to keep them in separate rooms and totally disinfect their environments as well, and always wash your hands very well in antibacterial soap before touching any other reptile or it's environment. Yellow Fungus is extremely hard to treat, the reason is that it grows both internally and externally. This is why it cannot be treated in only a topical, external way. In order to completely cure it or to even put a dent in it, it must be treated with prescription daily oral antifungal medications, daily topical antifungal medications, and typically they will also get monthly injections.
****Keep in mind that you may see an improvement in the infection externally while using only topical treatments, or right after he sheds the area. This is a common misconception that has resulted in the deaths of many dragons, because their owners are doing everything they can do to treat the infection on their own using only over-the-counter antifungal topical creams or sprays, often in combination with cleansing with an antiseptic like Betadine or Hibiclens. So they do this religiously 2-3 times a day for a month or so, and the infection seems to be going away, sometimes it does appear to completely go away externally, especially after the dragon has a full body shed, as the external lesions and patches typically are completely shed off. So then the owner is thrilled and either stops the topical treatments or continues the topical treatments just in case, either way the dragon appears totally clear of all signs of an external infection for a couple of weeks, then suddenly BAM!!! they wake up one day and their dragon is completely coated with the fungus all over it's body and is also suddenly very lethargic and refuses to eat. This is because the Yellow Fungus has been growing internally the entire time, and is now coating their internal organs and the entire endodermal layer. This is why I'm trying to create a sense of urgency for you to get him to an experienced reptile vet for the skin scraping test immediately, so that if he does have Yellow Fungus you can get him started on the prescription oral medications and topical medications as soon as possible, as this is his best chance to beat this horrible disease. I'm very, very sorry that this happened to you and to him, you both deserve much better.