When I was involved in this kind of work (within a Banking company), if we proposed a major new internal project or business unit we had to write a business case, and formally apply internally for project funding.
I recall my perplexity of how to do this the first time. It was for the funding to open a new trading group in one of our offices. I had to estimate the future financials for something that didn't yes exist. So how, based upon what?! The answer was 'Just try your best to use what might be
reasonable figures'.
180 degrees opposite of the usual 'To the cent' way that my head drives me towards re: figures. In the end it was in fact quite an interesting experience. Perhaps even slightly liberating, in that I discovered that I could produce financials of use, that were essentially somewhat-informed guesstimates.
I can use a similar approach now to my own private ventures. For rental
property I need x% net ROE to make a rental a viable proposition. For a purchase/develop/sell I need y% net. One thing that's most useful, is that it forces you to go with the head, the pragmatic side, rather the heart. Even the data for tax reporting on my property gets broken down on the tax return form into Income, and about 10 lines for expenses.
Similar principle for business planning.
Income
Variable expenses (further split down)
Fixed expenses (split into say 10 lines*)
Net Income
And try and project that for perhaps 5 years ahead.
The process itself makes you carefully consider issues that you had probably overlooked. So anyone starting out in business should be doing this process anyway. Particularly people who start out their venture by getting locked into $$$-rents and long-term retail leasing (leasing a shop).
You could find a person to do this for you. But he can only work off the data that you give to him anyway. And ultimately he has 'no skin in the game', he likely doesn't care a huge amount whether your business is optimally priced, and whether it flourishes or fails.
p.s. Before you even consider buying this business. I'd suggest getting 3-5 years worth of prior years filed accounts. And a copy of their lease. Maybe use that as a starting point for a business case style analysis