Depends on problem.
Allergists are trained to help with all sorts of problems, so it really depends on what you're making the appointment for. In terms of cost, if you're paying without insurance
or have a high deductible, you can simply call the office and ask for your "self-pay" cost.
They will give you an estimate for a consultation. If they do skin testing, that usually is an extra cost on top of the consult.