BB, $650.00 sounds like a fair price, and there is a bit of labour involved.
Does that include both belts, roller bearing, water pump? All these need replacing at the same time. (sorry re-read your post and you do include it). Do you use a 3/4 inch drive torque wrench and the crank lock tool? Easy enough job if you have those.
Attila, pays to have a crank pulley cog on hand also, a common failure, another US$68.40 + p&p, not too bad with the high dollar right now, and for peace of mind. Click the pic you will see the crack in mine around the keyway after 250,000km.

According to the collective knowledge of the Audi enthusiast forums, from what I have read imo, it's not known what causes the failure
exactly.
It seems to be a toss up between simply age/fatigue, but with great suspicion cast upon the practice of using a rattle gun to secure the crank bolt (which is common practice in New Zealand), but a rattle gun doesn't even approach the 450nm required for this bolt. I can tell you first hand that when we (my friend and I) loosened my crank bolt, it was not tightened to a torque of 450nm, according to my friend.. (it's hard to fathom how much 450nm is to the inexperienced like me, but we both undid the bolt (one on each side of the metre long wrench) and we both did up the bolt to 450nm and there was a big and noticeable difference between the two).
crank pulley part number: 034105263A
http://genuineaudiparts.com/partlocator/index.cfm?action=getJointLocator&siteid=214407timing kit
http://www.034motorsport.com/engine-components-audi-i5-20vt-timing-belt-kit-22t-aanabyadu-p-19588.htmlor they sell their own version of the crank pulley cog
http://www.034motorsport.com/engine-components-audi-i5-20vt-crank-pulley-cog-audi-i5-super-torque-p-13332.htmlUS$235.96 including shipping for the kit alone or, US$335.12 including shipping with their crank pulley.
Kit = US$235.96 = NZ$281.72, no GST no customs fees.
Kit + crank pulley = US$335.12 = NZ$399.855 - just under the $400.00 limit for customs to charge GST so if you are unlucky and the NZ dollar goes back down when your shipment arrives..., + NZ 15% + about $20-40 NZ customs fees, can't remember exactly what they charge but they do add a small fee. NZ$500.00 more or less IF customs charge.