Out of print, rare 80’s cassette tapes on ebay

I found this U.S based seller on ebay, he/she is selling 4 nakayama miho cassettes for $199. I've seen japanese sellers on ebay selling her cassette tapes as much as 250 dollars each. I've read somewhere that her out of print CDs, photo books and cassette tapes have been going up in value since her death. I'm about to send them an offer for $150. How much would you pay for these?