Iowa State extension sampled bedded barns at 12 different feedyards.  The average nutrient levels were 21.5# N, 13# P, 14.5# K on an as is basis.
At current Eastern Iowa fall fertilizer prices, that makes it worth $12.45 a wet ton.  Based on actual manure hauled out over 8 years at one location, that's about $100 a head space in nutrient value, and $60/head space after subtracting the cost of spreading.
My 2 cents, a bedded barn cash flows on cattle performance alone (so the manure is bonus); a slat barn requires manure value to cash flow.