Most business and general-practice attorneys could review your purchase agreement and tell you if the company is following it closely. For valuation questions, an attorney who brokers business purchases and sales may be more helpful. A Google search for "Maryland Business Brokers" turns up a bunch of hits; perhaps one of them can refer an attorney that they work with. The agreement review would probably be inexpensive, but (depending on how large the company is, how much information is available to you, and how detailed you want to get) the valuation may be more expensive.
As you might imagine, valuing a private company is more of an art than a science, and two different evaluators could give significantly different numbers based on the same data. Of course, the company's valuation will probably be much less than the valuation your lawyer or accountant comes up with. If you're lucky, there will be a procedure in your purchase/repurchase agreement that can be followed to come up with a "fair" number.
Congratulations on getting this far; people who own shares in private companies often get nothing at all for them.
With regard to the valuation of the shares, you should determine if the Board, or Officers, engaged any third party accountants to provide one. Also, you should review the agreements to determine if there is a formula for calculating the price per share.
I hope this helps.
Disclaimer: This answer is for informational purposes only and does not constitute general or specific legal advice, nor create an attorney client relationship.