Yeh its a pretty fiddly job if you've never done it before.
Especially if you don't have good tools (good quality ring spanners and breaker bar) since there's not much room to work with.
Getting it off isn't so bad but getting it back on again (properly) is a bitch
A decent mechanic should be able to do it in 2hrs comfortably. 3hrs max (including lunch)
I paid about $350 to have my timing belt, idler+tensioner, radiator flush, water pump and some other fiddly bits done and that was 9hrs worth of labour.....
so $550 seems like a bit of a stretch to me