@johnnyb82
Welcome to the expat.com forum and good luck with your potential move to lovely Bulgaria!
Bulgaria is still, I believe, the poorest country in the EU, so property prices and the cost of living are relatively low. But it depends where you're living now. If it's Germany or Finland, the difference might be dramatic. If it's Hungary or Romania, you might not be so impressed by the savings. The D visa process is not terribly difficult for retirees, so I don't think it's an issue to worry about (and you can apply at the Bulgarian Embassy in your current residence country).
I have legal residence in Cyprus and Spain too, and I can see big cost differences. The most noticeable is my electricity bill which is regularly 250-300 euros in Cyprus, but usually 35 euros here in Bulgaria.
As @tutisservis rightly says, you can get a criminal record check in the EU country you're currently living in. I don't know the exact BG requirements, and many countries want at least 5 years of criminal record. Hopefully, Bulgaria will accept it, but it's possible that 3 years might not be enough. You should show your residence permit of this country too, as this justifies why your criminal record isn't from your citizenship country.
You should also be aware that 5 years is a magic number in the EU. That's when you qualify for permanent residence in your current country, and this is an indefinite status which is quite hard to lose. Most EU countries become a lot more flexible for residence if you're already a permanent resident elsewhere in the EU. Indeed, there is a particular residence permit which is the "EU Long Term Resident's Residence Permit" which formally has some "freedom of movement" similar to an EU passport. The problem is that there is much confusion between this form of EU permanent residence permit, and the country-specific one... and not all EU countries issue both.
But, even allowing for these wrinkles, I'd suggest it's probably better to hang on for another 2 years in your current place, rather than starting from scratch immediately. Besides, nothing stops you from starting your research on Bulgaria, and even buying a property here (and spending 90 in 180 here, visa-free), while you're waiting.