Masters level player here that enjoys smurfing.
Can do the following leagues:
Silver / Bronze - roughly 80% win rate (last smurf run through silver into gold only had 1 loss due to 2 afk & no healer, but I can still consistently win with 1 afk or no healer on team)
Gold - can get you to plat league fairly easily, but will take more time as win rate is lower
Plat - boosting to diamond is doable but win rates may go down to as low as 60%
Diamond - only boosting to master if receiving an absurd amount of payment as it's less smurfing and more grinding
My schedule isn't super flexible, so payment model would probably look like X fg per win with caps that you set.