What you could do is look around at similar boarding places in your area to get an idea of the prices around there. Everywhere is different right now. Prices for hay, alfalfa, and food are different everywhere!
But, where I am right now...
Pasture board is 350. Includes: free choice hay in winter, feed all month, 2 feedings per day, blanketing if needed.
I believe full board is either 500 or 550. Includes: horse in all night, free choice hay in winter and a few flakes overnight, all bedding (maybe 2 bags of shavings a week? I'm not positive), feed all month, 2 feeds per day, blanketing if needed.
You really just have to look around in your area at the prices :) All horses eat different amounts, some horses need bedding changed more, etc. I know I'm not much help but maybe someone else on here can give you some more input! :)