Might check into what tax deductions you can get. There was a significant offset in 2010 for installing energy efficient appliances. Not sure when or if it ended.
Tax rebate amount was reduced from $1500 in 2010. I think its only $500 right now and the minimum rating that qualifies for a heat pump is 16 SEER.
Your energy utility may also have rebates for both smart thermostats and high efficiency units so check into it. Your state may also have tax credits.