I actually think if you go online and see the price displayed...that's the price you will pay (you don't subtract what you already paid for the seat). I think it's unlikely the prices will go down, however...
If you are a Spirit member, you may get an email link to bid on a new seat. I've done this several times and have had a lot of success, even bidding at the lowest value. I will say that I'm not sure how to access bidding unless you get the link...I've never been able to successfully find it from the website or app on my own.
You bid on either exit row or big front seat or both...you will only get charged for what you win, and it won't be both. You may not find out until a few hours before departure though, so don't despair if you don't see anything. I say this because one time I bid, didn't see that I won, then ended up paying for a seat and later find out I won the bid seat as well...but I got charged for both.
Another trick to remember is that Spirit will always assign you a seat for free. There is no reason to rush to check in EARLY, as you can constantly stalk the Spirit site to see what rows and seats are still available before checking in if you would prefer to be near the front or middle. If we are a group of 2 or 3, we stalk the site until we see a reasonable row that has 2 or 3 seats together, close to where we want to be, before checking in. Spirit assigns seats starting from the back it seems, so if the last row available is the minimum area you want to be in on the plane, you can always wait to check in when that row is available.
Best of luck to you! We are frequent Spirit travelers.
