Farm-to-table restaurant near Santa Clara Conv Center?
Parcel 104 in the Santa Clara Marriot is very close to your location, and they do seem to meet your seasonal/farm-to-table requirement. Their slogan is even "Seasonal farm-fresh American fare".
I have been here for dinner a few times and the food has always been great. It might be on the pricey side though (but nowhere near as pricey as Manresa), so not sure if it will meet your reasonably-priced requirement.
Unfortunately, frugal dinners and fresh, seasonal dinners have few restaurants in common; wish it weren't so.
Bradley Ogden has Yankee Pier at Santana Row, which is just a few minutes down the freeway. Most of my meals there have been fresh, seasonal, and good (a few clunkers occasionally). Check out their menu before going. Good luck!
355 Santana Row, San Jose, CA 95128