I think, JBL or Infinity would be the right choice here. Reduce the cost on HU, go for basic HU with USB such as Pioneer 3290UB or Kenwood KDC-MP443U (
http://acousticsforyou.com/store/car-stereos/kenwood-kdc-mp443u.html)
And buy a set of components for front : JBL GT5-608C
And 6-1/2" coaxials for rear door or oval 6"x9" speakers.
Subwoofer calls for an amplifier & amp. wiring kit & a proper enclosure and hence the cost would shoot up by 10K or so.
Remember, if you like deep and sweet bass, go for vented subwoofer enclosures - if you don't trust local makes, buy a subwoofer with factory fitted vented enclosure such as Rockford Fosgate or JBL .
Considering the budget, if you want to add a subwoofer sooner, I would suggest :
"a set of components for front : JBL GT5-608C
And 6-1/2" coaxials for rear door" first.
and later add the subwoofer.
Hope it helps.