I have a mystery ranch day bag that I like a lot, but man you pay a huge premium for modern camouflage patterns, molle attachments and fastex clips. I’m not at all across the variety of packs available stateside, but I reckon the best bang for your buck field packs are the vietnam era ALICE packs. They’re not as volume friendly as modern hiking style packs, but they’re light and rugged. Best of all they’re cheap as chips. I just did a google search and found this:
$85 man, 9 pounds, 3800cu in, will comfortably carry 70-100lbs. Molle is the ducks nuts, but you can just sew extra pouches onto the outside of the ALICE and it’s good to go. I know guys who use those packs to replace the ones our Army issues us. They’re fine for about 3 days I reckon, if you have to pack your own water. If you have a water source, the world is your oyster.
Might be worth your consideration. All the best with whatever you get though 😉