There are many consultants, brokers, appraisers and other experts who value businesses and cash flows. I do Most Probable Selling Price evaluations for my clients in most of the Western World.
The problem with a pre-revenue enterprise is that you'd be relying on projections.
Anyone who wants to buy a business is doing so because they wish to make money. This comes in one of two forms; cash flow from the subject business or savings because the subject business helps the acquirer save money.
Acquirers sometimes also consider synergies. For example: how much money could they make if they offered your product/service to their existing customer base.
The difficulty in the valuation process is deciding upon the reliability of the projections or trying to guess/estimate the savings or synergistic value to a potential acquirer who may not be known.
If you did want to hire a valuation specialist to create an opinion, it would likely have a stern warning to readers about the subjective nature of the input data.
Please arrange a call if you'd like to discuss your scenario and why you're looking for this type of expert.