
I too am a Jules Verne collector, and can tell you that though tough 
to find, it *is* out there.  I keep my eyes open all the time for his
books at various Bay Area used book stores, and every once in a while
get *very* lucky.  You just need diligence.  I don't know if the book
store situation near JSC is as good as the Bay Area, but good luck.
I have also had excellent luck at the Antiquarian Book Fair which comes
to SF every other year, though the prices are more in the $100-$200 range
than the $50 you want to spend.  My guess is that *if* you find it,
you won't need to spend even that much, since most people don't care 
about it.  I think I paid about $15 for my dust-jacket-less but otherwise
good condition copy, which I found one day at a small bookshop that happened
to have just bought a lot of random books at an estate sale.  

Of course, if you re willing to buy blind, you can put a $2 advertisement
in the Antiquarian Bookseller's newsletter (the exact title of which escapes
me at the moment.)  _Five Weeks in a Balloon_ is not the rarest of Jules
Verne books.  Someone has it for sale somewhere, and the AB is the way to 
find it.  In fact, I would be surprised if you didn't get multiple offers
of sale.  Of course, that takes the fun out of hunting for it yourself...

Good luck.