3 Choices 1 Offer

[kkaderlik]

I applied to three graduate schools in the US for their Art Therapy Programs. I got accepted to the best program and they want to know my decision before I even hear back from the other two schools (I have interviews coming up for the other two programs soon). The program I got accepted to is the most expensive out of the three and the only way I could realistically go there is if they give me a good financial aid package. What is the polite way to tell them I am excited about their offer but I am worried about the cost of the program and have more affordable backups in progress? But I would 100% go there if they make it more affordable?