Amazon have a good one on at present (well, they did a couple of months back, at any rate) for about £50
Gates and Conti as good as each other. Anything marked 'SKF' is fine, as the original GM stuff is, too. There have been issues with a slight squeak emitting from a pulley rubbing on the belt on the Conti kits (wish I'd seen the posts before I bought my Conti kit
) I have a squeak myself, but haven't isolated it as being definitely the timing gear, yet.
Usual stuff, don't buy second hand, because you don#t know when it'll give up. (though my theory on this is the 4 yrs/40k rule is broken down in the following - mileage affects the pulleys, passage of time affects the rubber belt, but don't bet your engine on it, it's just a pet theory of mine
)
Amazon, buy parts buy, euro car parts. Look out for discount codes. I bought a cambelt kit and added tot he order a brake hose for a few quid, which knocked £20 off the bill, by a 'spend over blahblah and get 20% off type of thing)
Other than that anything under £100 and you're on the money.