I have tried East Sussex County records, but they only came back with what I already knew: my 4xGreat Grand Mother Mary Feest/Feast - born circa 1740 -was living in Falmer when she gave birth to her (apparently) only child William (born c1771). Father William Hobden. Whether she married him is unclear, but her son William retained the Feest surname.
What no one seems to know is who her parents were or where she was born. I have found three Mary Feests that fit the bill, but they all were married elsewhere, and are only possible distant relations. Willliam Hobden is also an enigma.
But many thaks for your offer of help!! I hope you can find something!!