I just replaced a 17 year old Sears High Efficiency furnace that needed a $900 part with a Janitrol 92.5 Efficiency furnace that cost me $1100 installed! The contractor, whom I've known for 20+ years, swears by Janitrol so I went with them (he has two in his house, and hasn't had any trouble with them at all).
I figured if it costs half as much as a name brand, are you really losing anything if it only lasts half as long?
I thought it was worth the gamble. If I get 8 or 10 years out of it, I'll be satisfied. Anything else is gravy.