some things that affect "the value" of a quilt
 

emotional attachment
who made it - a relative, someone "famous", a prizewinner, someone anonymous
the quality/cost of the materials used (replacement value)
the workmanship
the intricacy of the piecing and quilting
how much one desires the piece

One more thing, condition, condition, condition (the most important factor, actually, when getting a quilt appraised.) An intricate pattern done in the best of materials with expert workmanship by a historically significant person is still worthless if it is in sad shape. Sad but true.

From my experience only a few quilts that have passed my way are "worth money". By that I mean very old, with the date, and in excellent condition and workmanship.
Justabitcrazy made some very good points.

Charity Auctions can push the price of a quilt to many thousands of dollars, upwards of $15,000 or more. I was there when it happened. In the end, anything is only worth what someone will pay.

As far as sentimental, there is no money to equal the value of my moms' hands on a quilt.

person a and person b could have made the same size quilt and spent the same amount for fabric and batting.

person a's quilt might be extremely unappealing because it was ugly and poorly done - even if the person spent many hours on it.person b's quilt might be exquisite.

my point - cost of materials and time spent on a project are only two factors in determining desirability of an item.

Brenda J. Grampsas, a certified quilt appraiser from Florida, showed some of her quilts at the Quilt Show in Dade City in February 2019. One of them she showed had exquisite workmanship - but - to me, anyway - was dirty and in poor condition. She said someone offered her $1700 for it!

The bottom line is - what someone is willing to pay for it!