300W PSU... ouch... Less than $150.. worse ouch...
Even my ancient computer had a 500W PSU... Now days I don't do less than an 800W PSU.
Well, I can't really help with that... all the old NVIDIA stuff is all deactivated and not sold anymore. I would have said like an 8800 GT or something, but I guess you can't find them anymore.
When you do go for new stuff though,
don't get a GTX 280 - they have a manufacturing problem that happens after forceware 196 which irreversibly causes the card to start dying, artifacting & freezing.
I have an
eVGA GTX 560 Ti right now, which is just a little better than the GTX 280, but it has DX11 support, which is what you're gonna want to have in a card when you go looking later. eVGA has pretty good warranties. They do dick you around and point fingers if you tell them your card's going bad though.
As for power supplies when you're looking later, I think the one I was liking was the
CORSAIR AX850.