illusions that can be performed (and viewed by everyone) for a crowd of about 100 people, as some of the people sit too far back to see the face of a card or a coin, chop cup scale or larger is ideal. Thanks.
Illusions generally refer to stage magic illusions like Sawing a Woman in Half, Spiker, ZigZag Girl, Sword Basket, etc. I'm not sure if you are using it in that context or as a synonym for a magic trick. If you are looking for low cost illusions, Andrew Mayne is the guy. Also, there are a number of inexpensive illusions that can be made with foam board in Mark Wilson's Complete Course in Magic. If you have a Genii subscription, there are a number of Osborne illusions (he had a column through around 2009). Also, there are a lot of illusions and parlor effects in Jim Steinmeyer's Conjuring column in Genii. If you are able to build you own, check out Jim Osborne's plans at:
http://hamiltonholtinc.stores.yahoo.net/plans1.html
All that aside, one hundred people is not a lot of people and you don't need large scale illusions to entertain that size crowd. That essentially is 10 rows of 10 people. Parlor effects like linking rings, sponge balls, egg bag, rope tricks, etc. will work fine. You could do a whole show from Mark Wilson's Complete Course. The Tarbell series also is a great resource for this.