The most important thing is that it be of good quality and not leak.
Finding a bargain my be a good thing, but you won't regret an investment
in a nice tray, it will serve you well. First you need to decide which type is best for you and your set up.
There are basically 3 types:
1. A slotted top that collects the liquid underneath in the body of the tray itself. You would then take the whole tray to sink to dump it.
2. Removable bottom tray. Some tea trays have a removable plastic bottom tray. Your tray can remain in place and you remove the tray liner and take it to the sink to dump.
3. Drain style with a hose. This tray drains into a plastic tubing that can run out of sight under the table, but you will need a milk jug or something to catch the liquid.
I have several trays but this tray, I have been very happy with. It just so happens to be a great deal. It is out of stock now, but they do restock often:http://shop.andaotea.com/products/wooden-tea-tray
Ebay is another option - sometime listed as Tea Tables.
Don't buy from Republic of Tea. The are notorious leakers.