Depends a lot on the type of menu. I've quoted some quick service restaurants 10 hours to write recipe spreadsheets with make instructions, inventory spreadsheets, ideal cost spreadsheets and prep lists. They wanted small manageable menus and didn't require a lot of sub-recipes. The same project for an oversized menu at a full service restaurant might be 80 hours of work. I estimate my time based on how many total recipes I have to write, allowing for 30 minutes for the ingredients and recipe procedure, 15 minutes to add ingredients to inventory and ideal cost spreadsheets and link them all together, and 15 minutes to organize the items on the prep list and proofread all of them. For quick service restaurants, I'll usually estimate less time per recipe.
Any research necessary or market testing is extra.
I charge $75 per hour for consulting services.