Hi, fellow marathon weekend planner here!
prices for 2018 haven't been released, yet, but you can make reservations now, and then pay when the full rates get released. Prices generally go up about 6-10% from the previous year's rates. So look at what's out now, add 10%, and you should get an idea of what marathon weekend will look like.
Also, Marathon weekend is not a value weekend for the resorts. It's not holiday rates, but it's not the cheapest. There
*MIGHT* be a sale off rack rates in September. It's happened the last three years, but like anything Disney, past results are no indication of future performance.
The DVCs are mostly gone, already. Last I checked, the only availability was at OKW and SSR, but that was 2 months ago. Once the monorail villas were unavailable, I gave up looking.
From what you're saying, you like the moderates better than the values. CBR and CSR are undergoing some refurbishments, with Caribbean Beach getting a huge overhaul. The renovations will be going through the 2018 marathon, so something to keep in mind. You might get a great rate for there, but you might also be dealing with construction as you're trying to sleep.
Most of of the normal CBR-CSR guests have been going to POFQ or POR for the marathon. The Cabins at Fort Wilderness is the other moderate on property.
If you want to make a reservation now, and are actually running in one of the WDW marathon weekend races, call 407-939-iRun to book your room.