If you compare that to the average cost of living in Japan it's a bit closer to $300 in terms of spending power.
Either way it's a lot cheaper than I'd expect to have to pay anyone for sex work, much less something that blatantly illegal.
Oh, as for the age of consent thing that change just made it a national crime. Every prefecture in Japan had already raised the age of consent to 16 (or higher) well before last year. The only places it didn't apply were some remote military bases and IIRC the portion of Antarctica that Japan claims. Still a good move but it's not like Japanese pedos were just having sex with 13-year-olds without consequence before then.