I would not rent or buy a used sleeping bag. It is nearly impossible to really wash and sanatize a sleeping bag and the "yuk factor" is just too much for me. A sleeping bag is a good investment whether you continue to backpack or not. I always carry a sleeping bag in my trunk when I travel, for emergency. If you hit the sales, you can get a good bag for about $250-$300 -- under $200 if you are really lucky. Just keep it under 3 pounds. You do not need to start out with a 900-down -- the 650-down bags are always on sale. Or a synthetic is fine for a starter bag. If you are 43 yrs old, and in good shape, you are capable of carrying slightly heavier stuff. You can pay an extra $200 and get a 2-pound bag that is as warm as a cheaper 3-pound bag. Only you can descide if it is worth the extra.

I never had a tent of my own until I had been backpacking for several years. I always went with people who had tents and just camped with them. Same with cook gear- just went with people who had all that stuff.

A pack is one thing that is good to rent or borrow. You can try several brands and models and get a good idea of what you will eventually buy for yourself. Same for a tent, if you want to sleep solo.

If you stay on trails, you do not need boots. Trail runners are fine. I think wool socks are the best- I use Smartwool socks. They are expensive, but then I wear them for everyday too so even if you do not backpack much, the socks are worthwhile. Lots of general sport store clothing works well. I find that the hunting-fishing stores have clothing at lower prices - just be sure to get the light weight clothes. Almost all backpacking clothing can be used for many other sports or wear as casual clothes so money spent on them is not wasted if you decide not to contine backpacking. My raingear and hiking pants and base-layers are my only backpack specific clothing items.

And I would say forget the SPOT, GPS or other expensive electronic gagets. Just learn to use a map and compass.