I used to have a service in the past, with great success, selling Riot Points for cheaper than retail.
100% safe and legal.
I know MaxCheaters's market is pretty much dead, but yeah, it worth a question to see if there are any potential customers.
The prices won't be like 50% cheaper obviously.. As I already explained it's something 100% legit and won't put your accounts on risk.
However, you can always buy RP on a bot account and gift to your main, to be even safer if that makes you feel so.
The prices will be something like: