For anything but accute edge warps, a decent record clamp will take care of it. Record weights will not take care of anything but mild warps on thinner records. I have made some simple clips out of brass wire that clip the edges of edge warped records to my platter. (see my system for pics of both) It is very tenuous grabbing the edge without getting in the way of the stylus on the lead in groove.
For a cheap alternative to the expensive Airtight noted above, you can buy two of the Rega P1 glass platter upgrades for $140 and put them in a convection oven at the lowest temperature for a half hour and then let it sit for several hours before removing.
For a cheap alternative to the expensive Airtight noted above, you can buy two of the Rega P1 glass platter upgrades for $140 and put them in a convection oven at the lowest temperature for a half hour and then let it sit for several hours before removing.