If you can put him in the 5 gal for now and keep the water pristine you'd probably be fine until you can find a good deal on craigslist. A common goldfish will quickly outgrow a 5 gal but it would work temporarily if you watch the water conditions.
I personally have a 20 gal overstocked right now with a comet and red cap oranda but they are both juvies and the comet is only temporary until my brother-in-law gets his pond built. I do twice weekly 25% water changes and have pretty good filtration.
I personally have a 20 gal overstocked right now with a comet and red cap oranda but they are both juvies and the comet is only temporary until my brother-in-law gets his pond built. I do twice weekly 25% water changes and have pretty good filtration.