I'd follow with the the user above me said. If you really want to see a boost in graphical preformance I'd hold out for something like a mid-range gpu which would run you around $200~
Because a GTX 750 from a GTX 650Ti is barely what I would consider an upgrade. If you're really cheap though I'd try hitting up craigslist and look for GPU's people are selling. You might find something to your liking.