Lets be more pessimistic, increasingly so:
1) Let us assume that the 860,000,000 ryo value from Kushina + Minato is correct. Lets assume that Minato (really J and Hiruzen, since its what he would have wanted) was a swell dude and donated 25% worth of this posthumously to ease the Kyuubi attack destruction. This gives us 645,000,000 ryo to work with as principle. Which yields (at 5% interest rate per year) about 1.2 billion ryo.
2) Perhaps we were not pessimistic enough. Maybe that interest rate is really 2% after misc. expenses (perhaps keeping investments afloat in ninja deathworld is a pretty expensive endeavor, and/or Naruto spends money like a fiend). This gives 830 million ryo.
3) Perhaps we were
not pessimistic enough. Maybe the Uzumaki were shit-broke by the time he was born. Subtract 300 million at the start. After the Kyuubi donations, this would come out to 420 mil ryo, and after 13-ish years at that crappy interest rate it comes out to 540 mil ryo.
Well, even in 3), Naruto should have approximately enough dosh tied up somewhere that liquidating a fifth of it would pay off our mortgage and keep our Hagoromo debt paid for 2 years.
Perhaps the J-man was just too prideful to ask him for a loan to buy the compound with to begin with?
(Does Naruto have a clan compound?)