Lucy
You'll definately have to get the RGK one - £100 sounds pretty reasonable in wheelchair cost terms
Access to work will definately throw stuff like adaptions and chairs at you if you apply - I've had a car conversion and one and a half wheelchairs out of them so far (about £7k). It's the one govt dept thats a dream to deal with. It's amazing what you can get if they think they can turn a benefit claimant into a tax payer
As I said before get as much camber as you can afford for width - find the narrowest door you regularly use - contact RGK and ask what the max camber you can have while still being able to get thro the door and they'll tell you how much camber you want - more than 6deg will look a bit strange on an everyday chair tho'
You can probably convince Access to Work that you need a entirely new Titanium chair with an adjustable camber bar though - I'd go down that route - all your issues sorted in one go - If you're using your chair outside a lot you'd be best advised to steer clear of folding chairs.