In The Phantom Menace, Qui-Gon Jinn is trying to get the parts he needs in order to repair Queen Amidala's ship. But despite the fact that he had plenty of money, it wasn't in a currency that Watto would accept:
Qui-Gon Jinn: I have twenty thousand Republic dataries.
Watto: Republic credits? Republic credits are no good out here.
After watching A New Hope, a similar scene involving credits caught my attention:
Obi-Wan Kenobi: Let's just say we'd like to avoid any Imperial entanglements.
Han Solo: Well, that's the real trick isn't it? And it's gonna cost you something extra. Ten thousand, all in advance.
Luke: Ten thousand?! We could almost buy our own ship for that! […]
Obi-Wan: We can pay you two thousand now, plus fifteen when we reach Alderaan.
Han: Seventeen? Okay, you guys got yourselves a ship.
It seems to me that Qui-Gon could have done a similar thing and just found a pilot that was willing to take them to Coruscant, where Republic credits would most certainly be something they would want. Repairing the ship would of course be better, but at that point there was no obvious way to do so and getting Queen Amidala to Coruscant was still a priority.
If 17,000 credits is a very generous offer for two passengers and two droids to avoid "Imperial entanglements", then it seems to me that 20,000 credits would be more than adequate for a handful of passengers (the "queen", Padmé the handmaiden, the two Jedi, and Captain Panaka, maybe a few more). And what's more, they aren't trying to avoid any "Imperial entanglements" because the planet is not under any sort of blockade, so they won't have to pay "something extra" for dealing with it. And even if that wasn't enough, Qui-Gon could certainly get more money once they reach Coruscant.
So why didn't Qui-Gon just hire a ship to take Queen Amidala from Tatooine to Coruscant?