Most amps of small stature are class D and they interfere with FM reception. A lot of them are less problematic with reception as they were a couple years ago though.

 

+1 on the RF PBR300x2 and Infinity Kappa 62.11i's. You should be able to get them for your budget. I ran that combo for awhile and it sounded good with no loss of FM reception on my '08 CVO Ultra. Make sure you set your amp gains with the engine running. If FM is important to you, do your homework before you buy your amp. Like others have said most class D amps will cause FM degradation because of EMI.