Having dabbled recently with a Dell Vostro 230 with a Q9500, I can say I agree with @emosun, you will be throwing good money at something that won't work out.
Those old Core2 systems usually had PCI-E 1.1 as well, so you're going to be limiting any card with a shred of gaming capability these days, even a cheap used one.
Something like this would put you way ahead:
Comes with RAM, Haswell i5, motherboard with an I/O shield even, and it would *probably* mount in that case as many of the Dells of that vintage were mATX.
Beyond that, sort video cards by Buy it Now and newly listed, I've scored plenty of decent, inexpensive cards that way. Maybe something like a GTX 750 Ti for $40-ish without an external power connector. There are also a bunch of HP OEM RX 460 2gb cards out there, about the same performance level as a 750Ti and I've bought one at $60 brand new.
It's not free, but having maybe $160 into a setup like that will be way better in the long run.