Paint Primer Question

I plan to prime, and eventually base, clear coat. I haven't stripped the old paint off yet but I know I will have some areas down to bare steel, others with body filler and other areas down to the original primer but not to bare steel. This wont all be at one time, I plan to do the car in sections and 1 year may go by until I can finish all of it.
What type of economical primer do you suggest that I can come back later and shoot with my base clear. This will not be a show car.

Transtar epxy primer,use on all bare metal and before filler is applied. you will have to use a good urethane hi build primer later on but the epoxy will lock it down. better stuff that cost more is PPG DP 90.