IGP = integrated graphics processor. You'll also sometimes see this abbreviated as "iGPU."
It dawns on me that you are running a Z97 board, so your CPU has to be socket 1150, which means it has to be Haswell ... that said, your i5, whichever model it is, really
should be able to handle HLSL no problem as all Haswell i5s have HD 4600 or better... I guess what I'm saying is something doesn't add up here...?
What resolution are you running the games at? 1080p? Higher than 1080p? Is your HLSL pre-scale at some ridiculously high value? (that's another thing to check in mame.ini)
I'm still seeing the ti around $125 - $130
Last I checked, that's still
around a Ben Franklin... unless you go by Price is Right rules.
I have the 750 Ti, bought it at $150 and haven't regretted it. You can indeed get it for less now. Maybe even $100!
But if all you're doing is Mame, what you've got
should be enough to handle the VAST majority of Mame games, with HLSL to boot. Can't say more without more info...