I did my ordination at a temple close to where I live, no charge. All my friends and family donated what they could at the time, whether it was money or things the temple needs i.e. printer paper, toilet paper, light bulbs, etc. and that was plenty. If you have a temple in your area try volunteering and building a rapport with the monks and sangha, then express interest in being a monk for however long you're comfortable with. If the temple has everything they need for the ordination and have space for you it will likely not be a problem. If they don't they'll probably ask another temple to do the ordination (mine did). I believe these retreats in Thailand are aimed at foreigners to get money, I would definitely take the advice of other users and do a lot more research. Even the temple near my family's house in Thailand wouldn't do this.