audio setup Qs....amp now or wait for HU

[Astrosfan]

I'm in a bit of a pickle and need some advice.

I recently got my car back from the shop and will need to spend $600 on a clearbra and tint, so I cannot justify spending $800 on a HU right now.

I already have some Polk db6501s in the doors and really really need them to be louder, plus i dont want to ruin them by having 4watts pushing them for much longer.

My set-up when finished will probably be a Kenwood dnx6180, polks in the front and a 8" or shallow 10" in the spare tire.

for an amp i was considering the Apline MRP 300 if it will push the sub enough.

So, should i go ahead and spend $160 on the amp (which i can justify) and hook the polks to it to satisfy my craving for now, or wait 6mos or so and get the HU? Im buying a amp at some point anyways, hopefully the MRP 300 can push a shallow poineer 10 or kenwood sub....

Thoughts, suggestions....?