As far as buying lumber from big box stores, it is always my last option. The price paid for lumber at these store is almost always the highest way to pay for lumber.
Decent lumber can be found in discarded pallets. Not all pallets are the same and it may take some looking but every so often a pallet used for machinery yields a fair amount of wood. You can look online to find the best and easiest way to disassemble a pallet, since they are put together pretty well.
You may not realize, but I read that in this country, more hardwood is used in the making of pallets then for anything else.
I live in Ohio, and once in awhile that a trip to Amish country. The area is loaded with pallet making companies and they will sell hardwood cut-offs or other unused pieces at a very reasonable price.
I’ve also had luck buying lumber at auctions. When someone downsizes or a company goes out of business the auctions they have or the sales they have can produce some good buys as well.
Good luck and keep your eyes open. You may be surprised at what you may find.