Tearing down old buildings will give you some nice lumber. I'm looking at one really old house now that has 1X12s for sheating on the roof and walls. Those are few and far between though.
You need to figure how much your boxes will cost if you build them and how much with shipping, if you buy them. If you live close enough to pick them up, they will probably be cheaper than building them without the shipping.
If you have to buy all your tools to get started, it could be cost prohibitive all the way around.
Even if you were to buy boxes and frames, there are still lots of things you can make like nuc boxes,inner covers,telescoping covers,screened bottom boards and slatted racks if you use those, observation hive, plus all the projects you can do around the house. I got a used Craftsman table saw back in the mid seventies. All cast Iron including the extensions. It's still going strong. As mentioned by others, a replacement fence doubles the usefulness.
Never go to lowes or hd for lumber. Go find a local hardware store. I get my staples for $10/5000, cd exterior plywood ($16/.5 inch, $21/ 5/8s), 1x12x8 6.50 or less, cannot remember, nails for $1.10 a pound, deck screws at 3.29 a pound, etc. I have saved TONS on money there. Lowes and HD are out to rob you!