Hey. 
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: 
  
1580 RP 
Retail: 10€ 
Me: 8.60€ 
  
4100 RP Retail: 25€ Me: 22€ 
  
5725 RP Retail: 35€ 
Me: 30€ 
  
8250 RP Retail: 50€ 
Me: 42.50€