Cheap things can still give you a lot of pleasure
I won't go there
As others have said completely subjective but as personal subjective opinions have been asked for.....
My Rockhopper was £600 new and my first proper bike if you will, used for commuting. Had everything I wanted and still does, more than paid for itself when considering the cost of busses and trains therefore VFM in that respect.
Like wise with my £400 Felt Z100 when I wanted a faster commuting bike.
Last year I bought a second hand Cube Attain for £1200. 105, hydro brakes, carbon frame. It's a hobby bike used for fun rides and for me the perfect vfm for a 'nicer' groupset etc
Currently looking at gravel bikes with hydros, 105 minimum spec at the 2k mark which I feel gives value for money for my needs.
For me I guess vfm falls in between all those price points and have found as I have stayed interested in my cycling hobby that price point has been raised to accommodate my growing wants/needs.
My regular cycling buddy loves wireless shifting, light as possible and is a specialized fanboy and has several 8k to 11k bikes which he feels are the perfect vfm for his needs.
My neighbour rides a £120 bso to work everyday and feels I'm daft spending so much on my bikes but appreciates it's my hobby and my bikes are nice. Each to their own.
Speaking generally I would imagine most people would be happy with a £300 ish, decent bike that gets occasional use but again lots of people on here riding years old bikes that they maintain and love.
Too many variables maybe to make fully informed comments about this but interesting to see everyone's opinion.