I built up two touring bikes using mostly new parts I found on sale on the internet but also used a few used parts that I found on ebay. On both, am using a used rear derailleur and used handlebars, one bike I have a used headset. But it can take months to accumulate the stuff you want if you are looking for sale prices to pop up. In the end I paid full price for all my rims, could not find any on sale. Just about everything else I bought was on sale.

Bought the spokes from a local bike shop, also paid full price for those. If you are building up the wheels yourself, shop around for spokes, the prices are quite variable. One bike shop was going to charge me as much for spokes as they would have charged to build up the wheels.

Finding a good donor bike may be the best way to go if you are more concerned about price than anything else. If you start going to garage sales looking for donor bikes, carry a caliper with you so that you can measure the rear dropout spacing to make sure that you get a rear hub that fits in your frame. For a LHT you want rear wheel sized for a 135mm rear dropouts. Some older bikes will have a seatpost that is the wrong size for LHT, but that is a very cheap part so if your donor bike has the wrong size, no big deal.