What's a simple, cheap treatment for my abdominal skin itching?

Hydrocortisone: You might try Hydrocortisone cream, which you can get without a prescription.

Depends: It depends on the cause, but over the counter cortisone cream is a reasonable place to start.

Depends on cause: For itching without rash, non-sedating anthistamines like loratadine, Cetirizine or fexofenadine can be helpful and are available without a prescription. If you have a rash, sometimes 1% Hydrocortisone cream can be helpful. It is best to consult your doctor to be sure that the condition is properly diagnosed and treated.