The GPR-109 from NAPA goes for around $24, and the MR-99 from Autozone goes for around $16. Both will do fine, and are parts for the older IDI diesel systems. There is a high quality Stancor unit out there for around $50, but for me, I carry a spare and would rather only spend $16. The life span will depend on how often you start the truck. I have a Glow Plug Relay Bypass System that I sell that helps prolong the life of the GPR, glow plugs and batteries, email me if you're interested.

The glow plugs can be a pain. If they are original, they may be broken off in the head which would require removing the heads. Not fun. Had to pull both heads off mine to replace them. That's the worst case. If they are frozen in but still intact, lots of penetrating oil should get them out.

Good luck.