Jeff (yet another Canadian on this list) contacted Uncle Chorn's Cabin last year for a price list (listed below).
Lophophora williamsii - 7-9 cm / 20 Euro . 10 - 12 cm / 30 Euro.
Lophophora williamsii v. cesapitosa - 7-9 cm / 10 Euro . 10 -12 cm /12 Euro.
Lophophora diffusa - 7 - 9 cm 30 Euro
Lophophora diffusa v. KOIKE - 7-9 cm 50 Euro
Lophophora fricii - 7-9 cm 40 Euro
It seems the prices haven't changed much - the L. williamsii plants pictured in the attached photos are sold for 30 euro each and have diameters of 10 and 10.5 cm accordingly (http://www.uncle-chorn.com/index.php?lay=show&ac=article&Id=5368749&Ntype=777
I have no experience doing business with UCC.