As far as I know they have very small discounts for registration. Not sure if they have for renewal.
Also in 5 month you can renew your domain name. I believe there will be no problem at all about that.
With the fierce competition on prices, Registrars are often registering and transferring incoming domains for the 1st year at loss. They need a way to recover such a loss and in general that’s at renewal time they have an opportunity to do so, offering another discount at renewal would jeopardize the system and would make very hard for the industry to sustain the model.
The renewal price you are paying is not excessive for a single .com even though you can find better deals if you do your own researches and you won’t need any coupon. Transferring the domain away is another option taking in account that a .com transfer is always coming with an extra year added on top of your current domain expiration date.
Discounts for renewals are a rare event as far as I know. Sometimes they mention some coupons in their newsletter, so you could still wait for a while, if you’re sure you won’t forget about it all.