If you know a commercial plumber, you can find a piece of PVC for cheap or a 6er of beer. 2'-3' is usually too short to use in that diameter, so it often gets thrown away.
Now you're looking at an $80 project to compete with that $200 retail pump.
Caveat is that you're likely looking at a 4" or 6" pump, as 5" is not a commercially common PVC pipe size. I do like 5" for a pump--4" is lower volume and takes a lot more time to inflate the raft. 6" is great volume, but takes quite a bit more muscle to push the plunger on that much air.
Follow the couple excellent DIY pump threads on here, and you can probably build a pump for under $50. 4" can be pretty inexpensive because the caps are cheap. 6" caps cost $12-15.
The hose seems to be the only spot you'll spend any real money.