I guess it really depends on what condition an item is in, as mentioned. But I would agree, not so much boots. Sleeping bag is a tough one, but if it's a good one and it's been well cared for it might be worth a shot.
Best option if available, as JW mentioned would be to rent some equipment first.
And you're right, good equipment ain't cheap and it adds up quickly. Good news is, with proper care it'll last a long time.