Affordable Design
The term “most affordable” is a relative term.
I imagine that the most affordable design is one that is honest, not pretentious, strives for perfection (where there is nothing left to be taken away from the design), and will not cause a wasteful expenditure (think of a multi-storey car parking structure with metal screens on it, air-con ledge that has aluminum screens on it that wants you to think that there is no air-con ledge behind it).
A good designer will even tells you that your proposed restaurant business is not feasible to go ahead even though you hire him for the interior design, tells you to rearrange the furniture in your house instead of buying expensive furniture and fixture, explains to you that it is worthless to change your furniture, your wallpaper from one style to the other because the method and procedure of experiencing the spaces matter more than the pure appearance of your wallpaper style.
But the problem: Will you pay an interior designer when he offers you the best answer, and it is to advise you to simply “move your bed”?
Would you rather pay a design fee higher than the construction cost because you want great advice?
It may sound easy but the answer to your problem could be comprised of honesty and a tremendous amount of consistency and experiences.
The fee for an interior designer is derived usually in a lump-sum, if not, usually 10% from the overall construction cost of the project, which is one of the reasons your project has so many redundant and expensive items that work like icing on the cake.