Here is a price list with links/part numbers (some are bulk pricing, some are subject to bulk discounts I haven't solidified with suppliers yet):
1 x 1/2" NPT Stainless Nipple: Here
is $1.72 per
1 x 1/2" NPT Stainless Female Tee: Here
is $3.68 per
1 x 1/2" NPT Stainless Coupling: Here
is $2.76 per
1 x 5220K78 1/2" NPT - 1/2"" tubing compression fitting (Brass) $3.14 (Volume)
8585K12 per foot is $1.17, this will depend on the vessel I am making the sight glass for
9396K286 are o rings that will be divided up into each order and a surcharge applied for each.... $.50 cents per o-ring will probably be it at an average of 4 per order.
Parts I need help with:
Stainless Eye-bolts (McMaster is just plain too 'spensive for these)
1/4" tubing - 1/2" NPT compression fitting
So, without those two, I see the total coming to about 20 bucks plus shipping (2-3 bucks per glass) which still puts the total at less than the one that Williams is selling. I plan on taking constructive criticism, suggestions, and sites where some of these things can be found cheaper.
Other parts will be added on a case-by-case basis and I am still trying to figure them out. If you want a sight glass with no tee at the joint, it will all be less expensive, but I am trying to work out a good/cheap choice for a brass compression fitting that allows a thermometer to be fit into the open end of the tee. The inspiration behind this whole thing is coming from Here