Second hand gearbox can be picked up from a scrap yard/ breakers for about £30 - £50. I managed to buy a complete engine and gearbox off Ebay for £10

, so might be worth looking there.
As Dave said, you can pick up a rusted Uno with good mechanicals for less than £50 if you're lucky.
Of course, if you buy a second hand gearbox you'll have to fit it. Do it yourself and save £££'s, or pay a garage to do it. I reckon a garage will probably want about £100 to fit, but shop around to get some quotes.
Also, check the workshop manuals to see if the 1.1 gearbox is the same as the 1.0. It probably is, so it will be much easier to find one as the 1.1 is not as common.
Why do you need a new gearbox?