Worth buying a wetsuit? How late do you guys swim outdoors?

On a very small budget and not competing but I love swimming outside and don't want to have to head back into the pool until I really have to.

Trying to figure out how much use I could get out of a wetsuit to determine whether it's worth buying one.

I'm wondering how late in the season people generally stay outside. And not necessarily the more "hardy" people. I'd appreciate any thoughts. Thanks.

Factors: I'm tall and lean (5'9" and 132 lbs) so I lose body heat REALLY fast - much faster than most. From both scuba diving and swimming, I've learned that I'm almost always the first to start shivering. And I've been mildly hypothermic a couple of times this summer during half hour swims in the ocean (I think the temps were in the mid-60's). So I'm on the "wimpy" end of the spectrum. I don't mind being a little cold during swims but I can't afford to take 2-3 hours to warm back up after each swim. And I've noticed I get a kind of dopey brain fuzz thing going on which is not conducive to decision-making and post-swim drives home. So I'm probably not a good candidate for just toughing it out and/or acclimatizing. Also, I have to work after swimming so I need a fully functional brain. :-P

If I could get a used wetsuit for around $100 and keep swimming outside to say mid-October then it'd probably be worth it. But I'm not sure how realistic that is.

Also, if anyone knows of any warmer bodies of water with either large roped areas or no boat traffic anywhere near Webster or Worcester, I'd love to hear about them. I've been swimming in Woodstock, CT where there's no boat traffic and no ropes but it's beginning to get a little cold already. I did go to Hopkinton State Park last week (just to hang out on the beach with friends) and did a little swim across and back there since it was (thankfully) not a guarded beach and it seemed much warmer than my regular lake. Is that generally a place where you can just swim back and forth (from the no lifeguard side)? Or did I just get lucky that day?