The El-Cheapo pumps REALLY ARE THAT BAD. I couldn't (and still can't) bring myself to throw down $160 - $200 for a good one and so I went through several cheap ones from Mall-Wart, my local raft shop (where I got a "Hyside" brand pump that was just as bad as the rest), etc. The cheap pumps all crapped out after a month or two. For awhile there I was pretty good at taking them apart and fixing the seals or re-attaching the dual-action air tubing inside the barrels - just what I like to do when I'm not boating...
I've always used an electric inflator hooked up to the car battery to air up the boat and then topped off with a manual pump. I ditched the cheap pump and got a foot pump to top off my boat a few years ago. The $35 foot pump has worked beautifully for several years and only now is showing signs of wearing out where the baffle is starting to leak. I've also replaced the cheap corrugated hose with radiator hose which will never crack and leak.
I recommend that you either:
A) throw down the big bucks for a good, high volume PVC pump if you think you'll be airing up the boat more than 12 ft from your car,
B) buy a $35 electric inflator and a $35 foot pump to top the boat off with (do NOT try to top off with the electric inflator - it doesn't work and you'll burn out the motor),
C) Spend $35 on about 3 or 4 consecutive cheap pumps, then bite the bullet in frustration and spend even more $$ for a good one or use an alternate scheme (B).
PS - I've heard of guys making their own pumps out of 4" PVC so if you've got more time than money, and a workshop that may be your preferred route. Sounds like a real PITA to me...
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse