Sounds like
Haramase Simulator. You don't actually buy them, you're paying to have sex with them and impregnate them. Part of a government program to increase birth rates. You just have to pay to start a session. After that, you can keep going till you're done or you run out of stamina.
You can get money from jobs, but the best way is to max the clicker game in the arcade and then go to the bank. Buy all the investments in the investment section, then deposit the rest into the bank. This will get you 10k per week from doing nothing. Its deposited into your savings account, so it will continue to increase if you don't withdraw it. Most of the girls cost under 10k, except for a few special ones like the cosplayer and some super late game ones which are many times more expensive (1 mil and 10 mil).
Also, don't except any changes, they update super infrequently since its all volunteer work.