What is the cost of electricity for drying a 30 lb wash load?

This is a good estimate, but your results will vary:
Assumptions:

• 30 lb dry weight load of cotton towels, 100G washer-extractor, dried in 45 lb natural gas tumbler
• Electricity cost = $0.12/kWH, natural gas cost = $1.00/therm

Huebsch Dryer Energy cost for the 30 lb load:

• Total energy cost to dry = $0.52*
  *$0.46 for natural gas and $0.06 for electricity

If you dry with an electric heated tumble dryer as the question states, it is much more expensive, typically two to three times the total energy cost of a natural gas heated drying tumbler. For this financial reason, almost no vended laundries use electric heat drying tumblers.