Most definately a rip off. There's still a lot of garages that are prepared to quote silly prices just because a car's an import. You are right in thinking that the running gear is Celica based. Get along to a decent motor factor that sells Blueprint parts and they should be able to cross reference a CV joint for you. Compare the old and new parts before fitting, especially the number of splines. Keep the receipt in case it's the wrong one. It's not a hard DIY job if you're ok with a set of spanners, and you should be able to do the whole job for around the £50 mark.