We've been running SuperHappyDevHouse for over 7 years and we have never charged money for admission. $20k is a lot of money to run an event, ours usually run in the $1-2k range.
Here's a breakdown of other costs:
--food ----< 50 people >>> (3 Meals at $6 pp) = $300 (sandwiches, pizza, bagel breakfast) >>> (3 meals at $10 pp) = $500 (with this you can get a well-priced taco buffet, pizza, snacks, bagel breakfast)
--drinks ----< 50 people >>>> $3 pp = $150 ....bubble tea would be much more pricey, but also much more awesome.
Also note that gummy bears can be purchased in 5 lbs. packs for $16 http://www.amazon.com/Haribo-Gummi-Candy-Gold-Bears-5-Pound/....