I have a suggestion for you, based on what I am guessing you are trying to achieve.
Let’s assume you have entities called Items each of which is related (one-to-many) to Quotes.
A Quote has a numeric field called Price, and a Quote is related (one-to-one) to a Vendor entity.
Set up a formula in Items which looks for the lowest Price (returns a number):
Now set up a formula in Quotes which checks to see if it is the cheapest (returns boolean):
Cheapest: Price == Item.Lowest_price
Now set up a formula in Items that finds the Quote whose Price matches the Cheapest (returns one (or maybe more) Quote):
Finally, define up a lookup field in Items that finds the Vendor(s) associated with the Cheapest_quote, i.e.
I know it sounds a bit long-winded, but actually, the helper formulas that you create along the way can actually be useful themselves in other ways.
For example, you might want a table filtered to only show the cheapest Quotes. Or you might want to calculate what percentage of the Quotes from a Vendor are the cheapest, etc.
Anyway, let me know what you think, especially if I have totally misunderstood your objective…!