Hi there,
I used Magowans tyres in Mallusk for a new back box on my Micra a year or so ago and have nothing but praise for the work they did. Their suppliers are next door so they can have pretty much any parts within an hour. The box was £65 fitted, the part if I remember right was about £50 alone so they were reasonable enough.
Magowans in Carrickfergus are meant to be useless FYI.
I'd stay away from Quickfit full stop, I've had nothing but trouble with them, that's just my opinion though.
Edit: Dee's exhausts in Newtownabbey gave me the cheapest quote but they didn't have the part at the time, I have no idea what the standard of work is like though. Sorry I can't help with anywhere closer to you!