What is mean by MMR ? Can you explain me more about your service.
mmr is "Match Making Rating", when you play dota2 it's 5 vs 5, and you always play vs the team with same average mmr (skill level - sort of)
You win a game, you get +25 mmr, and if you loose the game, you loose 25 mmr.
imho, anything below 3k mmr gets you terrible game matches, theres always some idiot that starts feeding after first death, 5 carry teams, no currier game, and so on..
5$ for 100 mmr is a reasonable price, even cheap, since 1 won match gets you only 25 mmr, and lasts about 45 minutes in average, but you should know that you are probably going to loose games you play on your own later with higher mmr if someone earned mmr instead of you.
cheers