basically u cant get the more serious stuff in this budget for both subwoofer and amp.
1 good woofer which could give competition to two subs can be
Cerwin Vega vmax 15
Alpine Type R
But i suggest u use small and 2 x subwoofers, more power margin more hard hitting. 15s dont give that rock impact, more towards low frequency
if u can stretch ur budget a bit another combo i can source is
jbl p1222 (pair) with Solid Audio f16d at 0.5ohm
but the one i told earlier will not break pocket and give a nice bang aswell the kenwood ref plus 9105d