organized group tour (Budapest)

Hi everyone. We are a group of professionals in Tbilisi, Georgia who are planning to visit Hungary during Easter next year. How much do you reckon will be the rent for a vacation house/apartment near the city center? lets say, 1 week to 10 days ?
Does anyone knows someone or travel agency who can give us invitation letter for a fee? Please let me know. Any help will be very much appreciated. email me pls Protected content