U R probably thinking of 44U & 44L Atlas figure new is $85.ish and go from there.
If he is using those, he might need a flask compress the 61a is for a single and they go for around $130.+ or the double compress 61b for around $130-160. Stay with the bronze stay away from the econ o $40-$55 they frequently don'e mesh and the pins are cheep. stay away from the ALUMINUM he might have processing problems aluminum is ok for injecting nylon but the heat rise messes up PMMA (acrylic). If he has a regular supplier sometimes U can talk to the rep and work something out. If U buy used flasks on ebay remember they are heavy for shipping but usually ok.
If he is doing dentures in microwave go only for new flasks.
If he is injecting his dentures U are in for $250-$700 depending on brand.
If he is flasking for pour system the Fricke POUR FLASK 4720-00 is a good long lasting choice but I have never spotted one on ebay new should be around $60,
Hope I didn't overwelm U this is not the whole answer.
Normal distributers Are Zahn, Darby, Patterson, Lincoln Dental, Pearson. probabily just search for flask.