Imo just go on eBay, search (t430,t440,t450,t460,t470,t480), click buy it now, sort lowest to highest, and scroll until you find one that's in good condition and has any parts you don't want to buy separately (SSD, charger, battery, ram).
The search term can include the t500s and other lines too, I've personally always stuck with the 400 models. So I can't speak to the x1 or 500 or other lines.
For Linux browsing you can get by on 8gb ram, but I'd recommend a minimum of 12, preferably 16.
Depending on your budget the sweet spot is probably t450 to t480.