The short answer is the advisor grants should be priced at the founder stock price. To use a different price, you would need a valuation, and given the size and stage of the company I suspect the cost of same would be unjustified. However, this question is worth discussing with a specific advisor or lawyer to the company, particularly since it involves tax issues, so my answer certainly has that strong caveat and this is not advice for any particular person or circumstance.
The Board of a company sets the Fair Market Value (FMV) for its stock and must exercise and undertake that responsibility, but in my experience, companies that are very early in their lifecycle as you noted below continue to set their common stock FMV to a low number that is at or near the FMV set at the founding of the company. The company might raise it marginally once they have raised some seed funding. There is some risk that the IRS or state or local tax authorities may find that the FMV for the stock issuance was too low and establish a tax liability for the individual and the company that is based on the spread between the price determined by the company and actual FMV, but this isn’t an area where we’ve seen a lot of enforcement activity in practice (it doesn’t mean that won’t change in the future however). If the company’s stock has a par value, the price per share for a stock sale cannot be below its par value stated in the company’s certificate of incorporation.
It is also important for the Company to understand that stock options are subject to IRS code section 409A and so we typically advise companies not to issue stock options until the company has paid an independent third party valuation firm to prepare a report for the FMV of the company’s common stock (usually $1-3K). Prior to that time, we typically advise companies to only use restricted stock grants, which are not subject to 409A. Unless the restricted stock is purchased for cash however, the value of the stock is taxable to the recipient and if the recipient is an employee that value is subject to withholding tax analysis.