Depends on area, if you know them, cash or card, how nice they are, how good they are etc...
Id do it yourself if you can or get someone to do it as its not too hard if you follow instructions. The hardest bit is getting the car off the ground for the exhaust parts.
I changed my old MG full system a while back and it took me 4 hours in total as i have never done it before, however it was a perfect job, no leaking rattling or anything.