I would just look to find an amp that can be bridged down. Just make sure that you are getting one that is the right Ohms to work with your speakers and the stereo. You are probably going to need to spend $200 at minimum something decent enough to drive those. Word of advice, don't buy used.
On one extreme, wire the voicecoils on each sub in parallel, so each sub is 2-ohms. Then wire the subs in parallel for a 1-ohm total. Use a class "D" digital mono block for efficient power, something like one of these: