There are a number of plinths on eBay. I would get one with a removable arm board in case you change tonearms. My reason for this is the plinth will be the biggest PITA to sell if you upgrade. So I would plan to not upgrade the plinth later.
I think you should buy plinth in the $800 - $1,000 range. A friend recently bought one and eBay and it was very nice, but not as nice as the ones from Woodsong.
You should spend the least on the cartridge, and maybe tonearm with a plan to upgrade later.
If it all does not fit in your budget keep the existing plinth until you can afford to buy something you will want to keep long term