I'm sure that you will get many replies, much better than mine, so I'll just reply quickly.
The main thing that the early C-22s don't have that the later 70's one do is a front hatch. The front hatch is great if you sleep on the boat. Air rams down into the boat and keeps you cool when you are sleeping at anchor. This is really nice! Not having a front hatch could be a deal-breaker in my opinion, that's how nice it is.
The early ones don't have a pop-top. The pop-top is a nice feature, but I wouldn't consider it a deal-breaker, since you mentioned that you are on a tight budget.
The mast is different, that is, weaker, on the early 70's C-22s. They are adequate, but you must keep your rigging adjusted properly. Most C-22 sailors don't have a clue on how to properly adjust the rigging, in my opinion, so this is important. Are you mechanical and patient enough to properly adjust the rigging to keep your mast from breaking on a really windy day?
Also, related to the mast, the spreader mounts are aluminum on the early C-22s. This was changed to stainless steel on later ones. This retrofit will cost you some money and and possibly a day change the aluminum ones to stainless. This is considered an important saftey item, from what I've read.
You stated that the sails were reported to be as good. I have never seen a mainsail from any sailboat with a motor that wasn't stretched out. Replacing a main will cost at least $500, so keep that in mind.
What motor does the boat have? That's important. It should have a 5 or 6 HP motor. A good modern 4 stroke motor is about $1200 ~ $1300.
A roller trailer isn't ideal. The ones with the bunk boards support the boats better.
Summary: If the boat is really clean, and you can get it cheaper, it might be OK, but you can figure that there will be things that you will miss when you look at the boat that will cost you money, so try not to over pay for it. Remember that there are boats that "free" is to much to pay for them. I recommend that you look for one in the late 1970's or early 1980's if you aren't in a hurry, and since summer is over here, I recommend that you take your time and find a better one to spend your money on.
Aldo