This vise here;
http://www.sears.com/craftsman-professional-4-1-2-in-bench-vise/p-00951888000P
comes with a base that will fit many 4" and 4 1/2" Wilton vises. You can buy one at your local sears and test it out. With on-line coupon codes I've seen the price as low as $110 in the past. (I have no idea what's out there currently.) Now, yes, this is more expensive than buying the base outright but you also get all the hardware to go with the base and it's all new. But here's the kicker, you can sell the top portion of the vise, eBay for example, as new and get a big chunk of your money back. I bet you could get almost all of it back actually. The bases on these are fine, these are 60,000 PSI castings and nobody will ever be the wiser.
Edit: And who knows, maybe the jaws will fit too, then you'd be way ahead of the game and have a brand new set of jaws.