I usually buy either Peak or Preston All-Makes when they are on sale and with rebate(s), the cost after rebate(s) usually around $3-4 a gallon concentrate which is a little as you can get now a day.
I bought 2 gallons concentrate Zerex for about $38 tax included from NAPA and used 1.5 gallons in E430. Since it will be in the car for 5-6 years, cost per year is about $5-6 which is very little.
If I can buy Polar LifeTime easily at local stores I may do, but driving around looking for it to save few bucks and wasting 2-3 times gas money doesn't make sense.