what amp do i need
 

i just bought a SWR-1243D sub from alpine its 4 ohms i was wondering if a alpine mrp-m500 would power it good? or is there another amp for a good price that would power it nicely

If it's that model it's a dual 4ohm voice coil model...meaning you can wire it to either 8 ohms(series) or 2ohms(parallel). So for amps, you need an amp that delivers 600 watts rms into 2ohms to get max performance from your sub...lots to choose from...get a good brand name amp, class d, mono will do the trick. That amp will work perfectly fine as well as it's 500 watts rms @ 2 ohms.

what amp would you suggest then?

Sorry...that amp is fine..if you haven't bought it yet than maybe you can get one that delivers a bit more power to maximize the output of the sub. There really are a lot of choices...rockford fosgate, pioneer, arc audio, ...really it comes down to your budget and availability. There won't be a noticeable difference in output between 500 and 600 watts anyway.

i know but there REALLY dang expensive....