I guess i have much the same advice as every one else that has posted. I have a few older properties require more maintenance than the new properties and here is what i have done.
1) I have asked the Real Estate Agency to never organise a trades person to fix something. They usually have a set number of people that are prepared to do what ever work quickly and for a very HANDSOME price.. I found it better Use my own set of resources.
Find 3 or 4 tasks you can use a benchmark for pricing. Ring around to a few plumbers/electricians/carpenters etc in your area and ask how much those tasks will cost. Choose the cheapest. Alway ask what the price will be for cash and how much will it be if you were able to source the parts required. eg pipes wires etc.
2) Go to a cheap printing machine andget some cards. Get some overalls and then open an account at a few hardware stored. I am not a builder or anything of that nature but i have an account with Reece Plumbing supplies and get everything at trade prices. This is usually 10 to 15% cheaper than normal. Ask what the trades person needs and ensure you have that prior to them turning up.
3) Once you have an idea of how much it will cost. eg if iyou think it will cost $100 then you call a plumber and say i have allocated $80 to the task etc. Bargaining always helps.
4) Use Things like eBay and the trading post to get items if possible. I managed to save $500 on an unsused still packaged air conditioning unit.

Krish