the really key thing here is not what the cost is but that the person that does the work knows exactly what they are doing and uses the right tools. Many garages will say they can do the work but behind the scenes will botch it by not using the correct locking/timing tool. Using this tool and using it accurately is an absoulute must.
I had my first belt change done at the dealer: they did a good job - no complaints BUT they were not spot on with cam 3,4. When I did it, I really fettled the timing on 3,4 and it runs better
so don't focus so much on cost but on whether the garage knows what they are doing: ask to see their locking kit. As them to explain the procedure for timing bank 1,2 to 3,4 - if they do not give a competant response - walk
I have just had my cambelt done by a friend/mechanic. Mine too was out on the timing, a tooth on the crankshaft pulley when camshafts were all aligned with their respective marks. It now pulls better, drops into overun (999.9 mpg displayed (I wish)) easier and gives better mpg!!!!
I used genuine parts, and included a water pump whilst at it. Lucky since the old one was leaking slightly and rough.
Two new cam covers and seals (old ones were suspect warped as breathers were clear)
plenum seals
6 plugs
cambelt kit
water pump
aux drive belt
oil filter
all came to a tad under £400 (inc discount). Thank fully I didn't have to pay for labour. A week later no6 coil went fut, £150 on two coil packs as well.
Get it done; properly. An extra bit of money spent on a quality job is worth it in the long run.