Figuring you have a monoblock amp for your sub, I'd recommend (for your budget) a Zapco ST-4X P 4-channel amp. You can currently get one for about $220 on
Amazon, sold by SoundsGreatUSA. SoundsGreatUSA IS an authorized online dealer for Zapco and anytime you can buy from an authorized dealer, that's all the better.
For the speakers, I'd get the Morel Tempo Ultra 602 two-way component speakers. I have these in my car and they are the best investment of my car audio system. They are quite excellent speakers. The bass is deep (for a 6.5" driver) and punchy the the highs are so silky smooth that you can listen for hours (even at high volume) and not get ear fatigue. You can get these for under $250 on
Ebay, brand new in box.