Littler, the world number one, beat unseeded Dirk van Duijvenbode 17-5, while Price defeated the Netherlands' Gian van Veen 17-10.
Littler opened an 8-2 lead and was averaging 117.10, a level that had him on course to pass Phil Taylor's record match average of 114.99 for the tournament. His scoring dropped in the closing legs and he finished the match with an average just below 111. Littler said afterwards that the pursuit of the record had affected his rhythm.
His tournament average now stands at 110.88, leaving him in position to beat Taylor's record aggregate average of 106.31 across a full Matchplay.
The win took Littler beyond £3 million in the PDC Order of Merit, more than £2 million clear of world number two Luke Humphries. He has averaged above 109 in each of his four matches this year and can become only the third player, after Taylor and Michael van Gerwen, to win the Matchplay in successive years.
The victory also extended Littler's winning run in matches of 20 or more legs to 28. His most recent defeat over that distance came against Humphries in the 2024 World Championship final.
Price reached his second Matchplay final. He broke in the opening leg against Van Veen and moved 4-1 ahead, before a spell of traded breaks left him 11-9 in front at the last interval. He then pulled clear in both scoring and finishing to close out the win.
The pair missed 23 darts at a double between them, and Van Veen was broken nine times in 14 legs on his own throw.
The result moved Price above Jonny Clayton to fourth in the Order of Merit, making him Welsh number one.
Littler has won the past nine meetings between the pair, with Price's most recent win coming in the first of their 2026 encounters. Price has never beaten Littler in a match of more than 15 legs, and Sunday's final is the best of 35.
Speaking to Sky Sports, Littler said: "Me and Gez always have great games. Gez will want to try and get me into a roaring battle. As long as I can get into the lead that will be the thing."
Price said he was happy to reach the final, but said getting one over on close friend Clayton had been his main focus going into the tie.
Sunday's final begins at 20:05 BST - follow the action live with Flashscore.