I changed mine myself the other day, it took me about an hour and a half, but some of that was chatting (I am not a mechanic). You can get to it from the top and it's a couple of 13mm bolts and a 15mm if I remember correctly. One is a bit fiddly but on the whole it's not too bad. Just take the battery earth off first!
Think a new starter is anywhere between £100 and £150. I had a spare so just changed that.