First, I have a Question... What's the difference between IG solar panels and AG solar panels and why do the IG ones cost so much more?
Now, on to the OP's question. I personally would get panels off eBay. I got 2 from eBay, and with shipping it only cost $168.00. The ONE panel I got at a local store cost $139.00. Installation isn't that hard, in fact, if you can cut and glue PVC, it's pretty easy! Even if you do have a Multi-Bank instalation It's not much harder. Just a little more pipe to run and maybe an extra valve if you really want to make sure you get even flow.
If you can give me some specs and measurements(panel size, roof size, number of banks, number of panels per bank/total) I can draw up a pretty good diagram including the plumbing and possible ways to run the pipes.
That being said, I LOVE my solar. I only have 47% Panel to S.A. ratio and I can warm my water from 80*F to 88-90* on a Full sun day(solar panels in full sun and running 9 hours).
HTH,
Adam