With books value is all about the Author, Edition and Condition, with first edition examples being signed by the author being at the top of the heap, sadly your copy of Pilgrim's Progress is none of the above, copies like this one from the late 19th to early 20th Century in poor condition list for under $10.00 at Antiquarian Booksellers at under $15.00
Re: This book is about 300 years old
Here are some links to similar editions of your book https://www.ebay.com/itm/115044926735?hash=item1ac936450f%3Ag%3AWMoAAOS…
https://www.ebay.com/itm/254950785483?mkcid=1&mkrid=711-53200-19255-0&c…
https://www.worthpoint.com/worthopedia/pilgrims-progress-john-bunyan-19…
https://www.worthpoint.com/worthopedia/1887-bunyan-pilgrims-progress-bo…
https://www.worthpoint.com/worthopedia/pilgrims-progress-john-bunyan-ny…
From what I’m seeing I’m guessing yours is from the 1880’s. Hopefully you can better match yours to one of the ones I found.
Re: This book is about 300 years old
With books value is all about the Author, Edition and Condition, with first edition examples being signed by the author being at the top of the heap, sadly your copy of Pilgrim's Progress is none of the above, copies like this one from the late 19th to early 20th Century in poor condition list for under $10.00 at Antiquarian Booksellers at under $15.00