FlAv, The gates kit (minus water pump) was around $55 bucks, the second car I did (my orange LS) the same kit came with the water pump for slightly more bucks. They were not the cheapest, cheapest is Dayco set that I know of, or ITM? I did both of them myself, so labor was $0. I selected Gates as they had the best install information, and exactly how to set the tension on the belt which seems to be the most critical step in the install process, get that wrong and the belt may not last till the next interval. However this would apply to any brand of kit you use.
Here is the paper by Gates that I found very helpful:
http://www.gates.com/oreilly/tech_ti...00411-reva.pdf
But use a kit you feel is best, I don't want to come off as a shill for Gates lol
Might be best to talk directly to the mechanic at the tire shop and ask him/her how many Aveo/Daewoo/G3 belts he/she has done and if they are familiar with the details. If they have never touched one, might be best to go shop around. The water pump should always be replaced during the belt swap, or at the very least a fresh O-ring seal. Reason being the timing set has to all come off to get to it, might as well swap it to save $ should it fail or start leaking.
When I did the first belt, I was so paranoid I wound up pulling the cover off, and rechecking the tensioner position and re-checked the water pump bolts after about 500 miles, as it was my first. I was able to sleep much better using a small (inch pounds) torque wrench on all the fasteners going back together. Hence why I like doing my own work, I can account for my own actions - or pay the price! LOL So I can relate to your concerns!