just speaking from a contractor standpoint. firstly i never lost money on a job i didnt get, but ive lost jobs because someone undercut my bid.truth of the matter is the lowest bid is not alway the bargan it may seem. take a good look at what you'll get for that price and what kind of follow up support can you expect.
when i was painting full time, my jobs werent done untill my clients said they were happy with my work.(clients Vs. customers......good contractors have clients. Mc Donalds has customers)and if my clients had questions or needed something touched up i did it. it was always factored into my bid as a potential need. like say someone bought a house and wanted it painted before they replaced the carpet. i always factored in a post carpet touch up in my bid.if the client did not want that available to them i would take that out, but many times the lowest big will only get you the lowest quality sevice and products.

PS keep the bottled drinking water,it'll prob'ly taste better than the city water. or at least keep the water softener and RO system.