All I know is the rubber membrane to replace the roof on a 30'x9' trailer is around $800. That is just the roll of rubber roof material, no labor, no glue, no seals, no vent covers, no seal tape, no seam caulk.
I could do my own but you may not want to tackle a job like that, my guess is around $2,500.
I priced the spray on roof for my trailer, it was $4,500.