Should point out to the last few responders, this thread is from last February. It was bumped by someone highlighting the price freeze for Man Utd due to commercial deals. There has been no comment from the club (at least that I'm aware of) regarding season ticket prices for next season.
I'm in a similar boat, the problem being my friends and I pay in a lump sum, and last season you had to renew before you could change seats. I have no idea how the refund works for those that buy in a lump sum, then move to a cheaper seat. The club does like to put refunds on your smartcard...