Hi Rochelle ~
I think that it is wonderful that you want to get a special gift for your son! It sounds like he certainly deserves it.
One of the things I love about being on the Disney Parks Moms Panel is that we are a team. Moms Panelist Lauren did some in the field research for me to help answer your question.
The Tea Caddy in the U.S. Pavilion at Epcot is such a fun shop. They offer Twinings tea, accessories, British sweets, cookies, and other royal memorabilia. There are 20 bags of tea in each box of Lady Grey Tea and there are 6 boxes in a case.
Currently, they are selling 4 boxes for $20.00 (keep in mind that prices are always subject to change). Unless you specifically want to get the Twinings Lady Grey Tea at Epcot, you may want to check some online sources as well to compare prices.
Please feel free to visit again with any other questions. We will be hEAR for you up until you embark on your pixie dusted trail!
Wishing you minnie magical memories with your daughter :-) Allison V.