seyz;
Don’t just go for the cheapest thing that works (even with a gauge). Go for durability because, probably, like a lot of us here, you are going to get inspired and stay with pumping for some time.
Some of these guys are very clever, mechanically. I can open the hood of my car and identify the radiator and the place to put windshield detergent; that’s about it.
They have some good home-made ideas. The tech side of that is explained here in several threads. Point is, you want to end up with something that is going to last you through a lot of use.