Putting Maps Together
First of all, other than the lab map, if you want to increase your pets stats (waste of money, I think), maps are useless. You will pay more for the pieces than you will get back in prizes.
If you don't want to listen to me, and want to do a map, buy the pieces individually. People sell "full" maps, but usually overcharge. Go to people's shops, go to like 20 of them, to compare prices on the pieces. Usually 1 piece will be very expensive, 2 will be pretty high, and the other 6 of the 9 pieces will cost about the same.
You can also make money doing this. Become an expert of the prices (within 100 points) of each piece of a map, and put them together and sell them as sets. The profit margin might be 5-10k per set, so whether or not it's worth your time, it's up to you.