The 24-year-old turned in a superb individual display as the Hammers fought back to claim a 1-1 draw at in-form Newcastle.
Chelsea this week set a new mark of £106.8million in bringing in World Cup winner Enzo Fernandez from Benfica, but Moyes believes the much-admired Rice would go for more than that.
Hammers boss Moyes said: "I don't know if I need to say the words, I think you can say the words if you watched it the way I saw it. I thought he was a top player in the first half, he really was, he showed so many things.
"Undoubtedly Declan is going to be a top player. Undoubtedly he'll be a British transfer record if he ever leaves West Ham."
Asked if Rice's departure was inevitable, Moyes said: "I hope it's not, I hope he sees his time here.
"But look, there's a lot of talk about it and when you see what's going about for the prices, I think Dec will be blowing that (British record) out of the water, that's for sure, when it comes around."
Rice's efforts helped the Hammers secure a creditable point on Tyneside on an afternoon when the Carabao Cup finalists sorely missed the suspended Bruno Guimaraes.
They could hardy have got off to a better start when, with Joe Willock having already seen a first-minute strike correctly ruled out following a VAR review, Callum Wilson ended his 10-game drought after being played through by Sean Longstaff.
However, the Hammers levelled through former Newcastle target Lucas Paqueta and then defended impressively to claim a deserved point.
As a result the Magpies, who remain unbeaten at home this season, slipped to fourth place in the table with Manchester United having replaced them in third following their 2-1 victory over Crystal Palace.