I can't say I've done many mods where I've saved money. Wait, actually I purchased a set of used Streamliner pegs off ebay along with an open box set of Kuryakyn floorboard mounted highway pegs. As it turned out, the floorboard kit came from Kuryakyn directly. I got the whole setup for less than $150.
I also bought the Kuryakyn LED Phase 7 and 4" passing lamps in ebay. Instead of bidding or using a buy it now option, I called the seller directly to negotiate the price. Along with free shipping, the seller matched the lowest price I found on ebay and on the web.
I typically negotiate labor cost with the dealer up front if I'm doing a big job. I have found that they will work with you especially if you are doing work that requires parts to be removed and reinstalled. For example, I put new handlebars on and did all the chrome housings, levers and grips at the same time. The cost of labor for the bars covered the cost for all the other items. Same thing for doing the chrome fork sliders, I had the lowering springs installed at the same time.