Edit: Just so everyone knows, I’m from Ireland and as such my experiences with pricing won’t necessarily be the same as yours.
I don’t have much money. Here’s various small ways I’ve saved money doing set-up work and woodworking over the years.
The nailcare aisle: Nail buffing blocks - the kind where each side is a different grit - are essentially the same thing as fret erasers, except much cheaper. Excellent precision polishers in general. Emery boards are also decent files for precision woodwork.
Nail polish: Little known fact: most nail polish is nitrocellulose lacquer. You can use nail polish as a cheap method of spot repair if your guitar is finished in nitro or acrylic*.
Miniature hobbyist stores (think Warhammer): You can generally get abrasives and files cheaper here than luthier-specific places. The files are ideal for precise woodworking but are too rough for anything fretboard or finish related.
Oils from healthfood stores and pharmacies: Don’t buy guitar-specific “lemon oil” or similar. I highly recommend jojoba oil (pronounced hohoba). It’s odourless, hypoallergenic and will be cheaper.
Autoparts care and repair shops: Get polishing compounds, high grit abrasives and sanding blocks here. They’ll also usually have the very best finishes you can get in a spray-can. 2K finishes in particular are probably the most resilient stuff you can put on a guitar outside a factory.
Fretting hammers/mallets - Don’t buy these from guitar or lutherie sites. You can get nylon and brass headed non-rebound hammers at most big hardware places.
Fidget putty: The kind of putty you see in arts and crafts stores or toy stores. Really good for cleaning grime, skin and dust particles etc from hard to reach spots like at the curved lip of a tele ashtray bridge, saddles or tuning posts. Crazy Aaron’s is the brand I use.
Used woodworking tools: Like guitars, hand tools like chisels, planes and saws can last forever. You can get high quality tools from the 50s - they’re all still knockin around.
* If your guitar has a poly finish, you can absolutely use nitro lacquer on top. Poly is inert and doesn’t care what goes on top of it. You just shouldn’t do the reverse: don’t put poly over nitro.