"We plan to be in Thailand for the December holidays and would like to rent a 2 bedroom condo (for 3 persons) close to DongTan beach in Pattaya (from Dec 20-Jan 9). Being this is very high season, I realize the prices are also, so would we like to be as economical as possible. Does anyone have an suggestions?"
This is the most expensive time of the year to visit Thailand. Most apartment - condo owners do not want to rent for short periods of time. There are many cheap hotels you can consider but it depends on your price range per night. There are serviced apartments you can get too. A serviced apartment will rent by the day or week.
What is your price range per night for for staying in Pattaya? You might get lucky and be able to use an apartment owned by an expat who is going home for the holidays. Regular hotel room, even during high season, can still be found under 1000 baht per night. But Christmas and New Years holidays will be tight.
This Expat Forum has some places for rent from time to time.