(For PC Only, as far as I know)
For anyone on the super broke end, who is simply looking for something functional that will last: for the past few years I've been using these generic "ps1/ps2 controller to usb adapter" you can find for about $5.00 online.
Old Playstation controllers for these are everywhere, and a lot of people have them already. They also tend to sit around in local thrift stores or online for 5-10$. afaik it's about as cheap as you can get a sturdy, long-lasting, fully functional controller for. Especially for one with an analog stick(s) and enough buttons for playing anything.
The main downside is that more and more PC games these days only recognize xbox360 controllers (Skullgirls is not one of these thankfully). I get around this problem using TocaEdit, personally. This adapter tends to register as a basic USB controller. Rarely you will also get random
haunted analog inputs for 2P's controller when nothing is plugged in there.
I used to buy PC logitech joypads, but I was finding that with heavy use, they were always dying on me after a year or two (went through about eight different models in the past 10 years until I swore them off completely).
And yeah this setup is ghetto, no you won't become Luffy (you can pretend though), and the dpad is slightly harsh, but it's better than keyboard. Personally I think it's better than trying to fit buttons on a snes pad or something, or having to use a 360 pad.
Disclaimer: You tend to get what you pay for. Most should consider this a last resort.