If budget is your primary concern look at used gear.  I have so many packs I don’t know where to begin.  I have a couple big Osprey bags that are my personal favorite for longer hiking trips but I got into the ultralight hiking and honestly my biggest pack (75L I think) is way bigger than I needed.  For me the 50l pack even hiking with my son and me carrying more of the gear was about right.  

A better way to start your search may be getting your packing list and see what you need to fit.  Some key considerations is you sleeping gear and spare clothing plans.  We used hammocks with a small folding piece of insulation and lightweight rainfly/sleeping bag and that was the heaviest and bulkiest thing to carry.  From there 2 extra pair of socks and underwear and that was it for clothes.  Stove I used a MSR pocket rocket with 1 can of fuel and a Heineken Pot and mountain house dehydrated meals with trail mix as snacks.  Where we hiked there was stores we crossed often enough.  

We hiked the AT for 5-days straight and my son was 13/14 at the time in early June as I recall.  I wish I could find my old notes but  I recall my pack weighed about 30-35 pounds loaded which is actually quite heavy for AT hikers.  Loot at what through hikers on the AT pack and some are down to 20-pounds and they go for months on end.  

Anyways, the smart thing to do is better define your goals.  Then try to make a packing list and try to get a weight/size idea of your load.  That should drive what pack you buy.   Now, as I started saying, used packs are awesome as I’ve got a bunch of $300-400 packs I bought used for say $50 that may show wear or have patches etc but it lets you try them and figure out what you like.  The extras end up getting packed as emergency bug out bags or resold for what I paid for them.  Some people are proud of their used packs and try selling for nearly new prices but be patient and you can get some really great stuff for reasonable money.

Sorry so long winded.

Edit to add:  you absolutely need to get measured and look at the specs for the pack too.  I am about 100-pounds heavier now than when I was doing a lot of hiking and how a pack fits really matter for long adventures.  Once you get measured you can check the specs for almost all packs online to get an idea if it will fit you.  It’s always best to try it on first if you can too as chubby me at 6’4”” 290 doesn’t  fit the same as I did at a very skinny 190.   I also found I strongly prefer internal frame packs but I have at least two external packs that have had a lot of time in the woods.   External frames are great to tie shot on as we did some trail maintenance hikes with scouts and it worked well to carry axe, saw and other awkward stuff.

oP, you never gave us a season.  Are you only using this in summer where you don’t need a warmer sleeping bag and extra clothes or are you looking for 3 season to include chilly spring/fall or possibly 4 season which require a much bigger pack?

Do you hike where it rains a lot?  Of course you can get a rain cover for any pack but there are some new synthetic materials that are just about waterproof on their own.  

What kind of pack are you interested in, standard weight, lightweight or ultralight?   Here you might Google what through hikers on the AT are using as it really is a good way to appreciate how small a pack you can use if you choose good gear  

As for the Maxpedition gear suggestion above, i have lots of maxpedition gear but that stuff is seriously heavy for hiking.  I use those for day trips or motorcycle camping and I would strap my big Maxpedition Vulcan to the back seat but unless you like to torture yourself there are far better options for extended hiking than any of the tactical type packs.  

Beyond Osprey another brand I personally like is High Sierra and I have an internal frame and external frame pack by them that my sons both used for Boy Scouts and I used the external frame pack hunting for years so I could pack in outer warm layers and strap the gun with extra layers in the pack dragging deer out of the woods.  

I bet I have a dozen to two dozen packs if I dug them all out and everything has advantages/disadvantages but as I said Osprey as a brand has been my favorite.  I bet I have four of those in various sizes from 35l to 80l.