Haven't worked that end myself, but it is an interesting question.
According to this source, the average in the US for almonds is 2 hives / acre. http://www.rirdc.gov.au/programs/established-rural-industries/pollination/almond.cfm
For blueberries, 1 hive per 2 acres (1/2 hive/acre) up to 2 hives per acre. http://berrygrape.org/blueberry-pollination/
Fees per hive for pollination in almonds was around $80 a year in 2005, but has been around $150 a year in 2008 and 2009. The price of almonds and the number of beeks who show up with hives affects the pollination fees quite a bit. http://www.beeculture.com/storycms/index.cfm?cat=Story&recordID=666
In Canada (where their dollar is about equal to ours), hive fees for apple and blueberry has been around $100 while canola has been around $120 to $160. http://www.honeycouncil.ca/index.php/managing_bees_for_pollination
Not sure what crops are closer that you would go after (pumpkins, melons, peaches, etc) or what they typically pay.
Assuming $100 per hive, you might be able to gross $2400 for 24 hives. Assuming $150 per hive, you might be able to gross $3,600 for your 24 hives. Then you need to subtract your costs.
How much does it cost to move your hives to the site and then back again? Standard rate for travel in a passenger vehicle is $0.50 a mile, a flat bed truck is probably going to cost more. Is overnight travel involved? Will the stress on the bees possibly reduce your income from the sourwood?