You can purchase a rank here -> https://buy.mccentral.org. They range from $5 to $110 (I don't know if the sale is still on but won't be on for long)
Yes the 40% sale is still in effect, though it won't be for much longer. Unless alex decides to extend it to be longer than 48 hours, which seems to happen a lot. Would still be better to get everything you want as soon as possible though. Also as another method to get a donator rank, you can also pay someone in-game cash to buy you one. That way you can get a rank or rank upgrade without having to spend a cent of real money. Just be wary of scammers.
