'Strongan' is Zodiac's euphemism er - trade name for PVC. I'm pretty sure all Cherokees came with PVC tubes that have thermobonded seams. I'm not sure what can be done with thermobonded seams once they start to leak.
Who quoted you $ 10,000 for a set of replacement PVC tubes?
Have you tried Inflatable Boat Sales in Delta?
I'm sure Guy over at Polaris Inflatable Boats in Langley could make you a set of proper (ie. hypalon) custom tubes to fit your cherokee for waaaay less than 10 grand - or he might have some other economical recommendations for you.
Good luck - let us know how things go.