I would suggest that you create a set rate chart and have it prepared and ready to present to inquiries. Most people spend about thirty seconds making the final decision to take the plunge and contact a potential VA - it's up to the VA to jump in and respond with the ready information the client needs to make a decision.
I've hired virtual help in the past and didn't have the time to follow up with those who responded with a question to my own question. I wanted answers!!
In order to take advantage of the potential client's interest (it may not be too late!) figure out what your standard rate is for general admin services and maybe write up a little note about that and include info on a few of your specialty rates.
My best overall suggestion is to never answer a potential client's questions with a question - it's the same thing as putting up a stop sign....