The sweet spot for me seems to be last year's thinkpad + all the parts needed for a complete refurbishment + upgrades.
eBay thinkpad: $400-$800
ssd: $150
new battery: $100
(As needed)
new keyboard: $50
new trackpad: $30
new plastic parts: $140
new hinges: $20
new display: $150
ram: $100
You can spend more on the laptop and skip some/all of the cosmetic refurbishment, or spend less on a junker and replace everything. Either way, you can end up with a "looks and feels new" machine for around $1000 that would be comparable to a $1500 - $2200 model if you bought it new.
It's also kind of fun.