I would go for the better vise, its just one of those tools that it pays to get the best you can afford.
On that note have you looked at the Glacern 4"?
Glacern Machine Tools - All Products
Its been a while seens I have bought anything from ebay but I am thinking that buy the time you pay all the extras it may be as cheap to get the Glacern which is said to be a better vise.
Ofcourse if you go the cheaper route LMS is a good place to buy. I am not sure if maybe a 3" might be big enough for you but LMS screwless vice is a very good vice for the money. Even though this vice is rated as 3" width it opens within a few thou of the 4" vices. These vices are a bit more sturdy than the cheaper one listed. Although the Shar's and Glacern version are pretty good units.
LittleMachineShop.com - Vise, 3" Screwless with Clamping Slots
The heck of it is a man needs more than one style/size if its possible. Or even double matching depending on what jobs are being run.