I've been buying old gas grills, rehabbing them & either keeping them or selling to friends for what I've got in them.
This is a recent source of entertainment , definitely not for profit.
I've gotten a master forge , a charbroil , 2 old weber Genesis ( oldest 17 y/o) , 2 weber Q's & a weber spirit (16 )
I've learned a few things .
A failing firebox is a terminal event! Not worth trying to jury rig burners & manifold!
Frames go bad ( old webers the back of the frame has a design flaw)
All flavorizer bars ( heat shields) eventually fail even SS
Porcelain coated grates eventually fail although last longer than the heat shield.
In affordable gas grills cast aluminum firebox is the best option.
Stainless body vs. porceloin coated body makes minimal difference.
Weber parts , both factory & aftermarket are easy to find even for 20 year old grills
Aluminum baking pans are useful for making grease pans & a lot cheaper than factory part!
So these recommendations have nothing to do with cooking ability just longevity & ease of repair.
Under $500
Weber Q series , these are so simple to work on almost no parts , cast aluminum body, the grate is the heat shield , the frame is plastic & can be replaced for $80! My new used q320 will be around for my great grandchildren to use !
Weber spirit series & several models of Broil King /Mate run below $500 easy to repair & parts easily available !
$500 - $1000 weber Genesis series ( the porceloin enamel will last as long as the stainless) again Broil King has several models and may offer a little more bang for the buck.
Do NOT buy the various store brands sold at HD, Lowes or Sam's!
There are dozens on Craig list 3-5 years old selling for under $100 & some simply for hall off! The Mastor Forge I got had hidden firebox damage even though only 3 years old!