Depending on DIY or pro auto labor, you will have $500-$1000 in front end rebuild (steering/sway experienced) if the "pop/clunk" while turning is attributed the wheel hubs & not the ball joints, add another $250 or $500 also dependant upon DIY. Add new shocks (assuming this isn't air-ride/electronic suspension) tune-up (spark plugs/wires/MAF & TB cleaning) and complete fluid/filter update all the way around, another $500 after all said & done. That's what you should expect to put into this vehicle not including any "check engine" or sensor-related faults that may arise. You should be asking for any labor tickets,receipts and whatever maintenance records this guy has. Explain to him what all this truck needs to make it completely reliable and take exactly $4k in large bills with you. If somebody wants a $7,000 '05 tahoe, then let THEM buy it. Rust, poor handling & any popping noises is an easy $1500 deduction right off the top. There are a million tahoes for sale, I'm sure he can appreciate that you are interested in his. Look up some more trucks and print off what you have at lower price points for even more ammo & then he knows you are seriously looking around.
I think you should invest your time wisely by doing research & looking at several other trucks to get a better idea of what is out there. Or just wait for a way better truck/deal to come along. It took me over 2-months to find my last truck.