Getting a third bid would give you a better picture regarding pricing. Have you seen the work of either fabricator? There have been enough "bad seam" posts on this forum recently to make me think twice about hiring an unknown.

I got seven bids from fabricators and countertop companies and narrowed it down to two before the interior design company mentioned they also sell countertops. I haven't seen any of these companies finished product.

Undisclosed fabricator is a red flag to me. I'd use the comparable bid for the company that comes highly recommended. I don't see any upside going with the interior design company for your countertop

"I haven't seen any of these companies finished product."

That is the most important deciding factor in selecting a company. How can you trust someone to come into your home and provide a good service and quality of job without looking at the finished product or getting referrals?

Interviewing doesn't mean jack without seeing their finished work. There's a lot of very skilled Larry Liars out there that interview very well but do their work with a garden hose in a shed somewhere and have no insurance if they drop it on your floor and smash it.