Agreed with Tom. Also, if you're concerned about affording two individual tanks, you can always check craigslist -- I've purchased 40gal+ tanks on there for cheap from people who want to get rid of them because they are moving, are upgrading, etc. I just purchased a 100gal tank on craigslist for $80 -- anyone can tell you that's a great deal, so look because you never know what you will find!!
If you get a tank from craigslist, just make sure you clean it out well (ideally with a 15% bleach solution to allow for maximum bacterial/fungal disposal) and let it dry and allow the smell to air out before you decorate it.
Additionally, if space is a problem (e.g. you don't have enough room in your current apartment for two 40gal tanks), you can look into custom enclosures that stack two cages vertically instead of horizontally. However, custom enclosures are typically expensive and difficult to assemble upon delivery, so you're going to have to choose between the variables of space and money. The happiness, safety and well-being of your beardies are not a variable you can alter just because you can't afford the upkeep. You owe it to your pets and yourself to make sure they are well taken care of -- you cannot put your wants over the needs and well-being of your animals. If you can't afford to do so, you need to start looking for a responsible person to adopt one of your beardies to help you minimize your spending. Not to mention if money is a concern for you, housing a female and male beardie of reproductive age together can result in baby beardies; taking care of a litter of baby beardies is only going to exponentially increase your expenditure.