In Paper Mario, a shady character named Rip Cheato sells you items for 64 coins in the last room of Toad Town Tunnels. He has a few Star Pieces for sale, but he also has junk items like the Dried Shroom.
The pipe in his room leads to the blue locked house in Toad Town near Tayce T.. The pipe makes a convenient secondary entrance/exit to the tunnels.
The Items are always acquired in a set order, as follows.
1st purchase............Star Piece
2nd purchase............Life Shroom
3rd purchase............The Bump Attack Badge
4th purchase............Repel Gel
5th purchase............Star Piece
6th purchase............Super Shroom
7th purchase............Mushroom
8th purchase............Dried Shroom
9th purchase............Dried Shroom
10th purchase...........Star Piece
11th purchase and on....Dried Shroom
That's 640 coins in total to get all three Star Pieces. Better get saving.