I nearly always go to Kwik Fit, granted their tyres can be more expensive than some other places, but with the branch near us I can 'guarantee' they will do a sopt on job.
I had a similar problem with a screw when I had my 1.4 Clio, they just removed the screw, made the hole slightly bigger, cleaned the inside of the tyre and the hole, then plugged it with a solid rubber plug, did all the powder dusting and stuff, job done! I never had any problems with it after that.
You really shouldn't expect to pay more than £10-£15 for a repair like that.