Not much chance of finding a lower price on 100mm illuminated buttons than $4.93 (the price right now) on those "Aftermark" buttons you linked.
My only
possible concern would possibly be the quality/reliability of those vs. the Happ buttons.

Divemaster127 (Gary) has Happ buttons
here that look like that size.

Happ page for that part is
here -- 2nd photo has dimensions.
Don't order direct from Happ -- they are infamous for charging outrageous shipping costs.

Scott
P.S. There are some european suppliers that carry them, but not sure where you are other than "not Canada".
