You'll be surprised to find how may other cars are out there on the road sharing the same diff/gearbox as you're own car. Even though it's a suzuki there will be many other suzuki's out there with the same (or similar) bits as yours.
My advise - spend a day out around the local scrapyards and try to find how many different suzuki (or other manufacturers') FWD cars share the same gearbox/boltpattern as yours, and then do a bit of research on the ratios available.
For example - Both Toyota and ford used the same rear axles for years, and for a short period of time, the same gearboxes too. the same goes for Honda/Rover and Daewoo/Vauxhall, Peugeot/Citroen etc.
If you're lucky you'll find a gearbox that'll fit, and with a bit of haggling, it could be yours for £40-100 (depending on car/condition).
I'm not all that sure about suzuki parts compatability but it's gotta be worth having a wander around you're local 'yards to see what goodies you can find. you'll usually come away with an idea about what's possible. I always head for the scrappy if I'm stuck with what to do on a project. they're highly inspirational places for grease-monkeys like me
and remember, Nothing is impossible, but you'll usually find a better (cheaper) way of doing the job another way.