You certainly should be able to build your own table as heavy as you desire, purchase all new drive motors & other electronics including a new desk top computer & all software to compete with most anyone elses packaged software, new bearing rails, etc. for well under 10,000.
If you scrounge around for & purchase your precision bearing rails & various other items from ebay etc. There are plenty of relatively inexpensive CAD CAM softwares that will easily handle the 2D needed for Plasma/OXY FUEL cutting & you don't feel you need automatic nesting of parts, You can build a very nice, industrial quality even, table for around 6,000. There are people on here that have operational tables, built pretty much from items that are salvaged 1 piece at a time. They may only have 1,000-2,000 in them.
If you have the ability to build your own table, (place to build, time necessary to build, Tools needed, etc.) Then yes I feel you can construct a plasma/torch table equal to if not better than most anything in the $10,000-$20,000 price range.
Look through the many build logs here on the zone. If you spend several hours reading you will gain loads of info on what it takes to build a table. You will also find many people willing to help you answer questions.
It's not something you can build in a couple weekends, probably not even in a couple weeks. I have many many hours in mine, didn't even try to keep track. I spent loads of time to make my table both easily repairable & even expandable if needed.
Keep in mind it's impossible to tell what tomorrow may bring through your door. If you think 5 X 10 is large enough then build at least a 6 X 12. You may even want to concider building your gantry to handle both plasma & ox/fuel. You also have to give thought to how large/heavy a sheet of plate you can handle to get on your table (Forklift, overhead hoist, size of your garage door etc.
If it works.....Don't fix it!