@longtimedisneylurker already posted last year's prices. The website or cast member on the phone charged us $101.94 (9% tax and 18% gratuity included) per adult and accordingly for kids. As with all things Disney, prices may be higher this year. You can charge it on a credit card or Disney gift card.
I feel the quality and variety of food at the feast is far better than what you might enjoy at any other character meal any other time of year -- and maybe even on Thanksgiving. There are salads, fruits, breads, cheeses, charcuterie, cocktail shrimp, smoked salmon, and crab legs, soups, a carving station with beef and turkey and traditional Thanksgiving fare, a kids meal station with pizza, nuggets, macaroni & cheese, a made-to-order pasta station, desserts, crepes and fondue stations, etc; soft drinks with refills, coffee and tea are included. The hotel ballroom is large and grand; the lighting and decorations are beautiful and very festive. There's a live band that plays renditions of Disney and holiday classics. There are meet and greet spots with festive backdrops throughout the ballroom to meet and take pictures with Disney characters. If you decide the Thanksgiving Feast in the Disneyland Hotel is too much, there are less expensive character dining options on Thanksgiving Day at the Storyteller Cafe, Goofy's Kitchen, and PCH Grill.
Here's a good Thanksgiving Feast thread from last year:
https://www.disboards.com/threads/fall-harvest-thanksgiving-disneyland-hotel.3549570/