Bubbles Naggenvatcher

http://www.tf2outpost.com/trade/19325502 - sold for Aces Cowl (price is old, should be closer to high end)

http://www.tf2outpost.com/trade/19186605 - sold for Smoking Bloke's + Pro S. Bazaar + ~2 keys in sweets (~1)

http://www.tf2outpost.com/trade/18624809 - sold for 1 bud (~1)

http://www.tf2outpost.com/trade/19317185 - sold with other things for TW Shanter

http://www.tf2outpost.com/trade/19087997 - sold for Aussie Sticky (~1.4)

http://www.tf2outpost.com/trade/18981261 - sold for Bubbles Slug + Robo Sandvich (Dat outlier)

http://www.tf2outpost.com/trade/14730970 - sold for 34 keys (~1.7)

Bazaar

http://steamcommunity.com/market/listings/440/Strange%20Professional%20Killstreak%20Bazaar%20Bargain - average ~$10

http://steamcommunity.com/market/listings/440/Mann%20Co.%20Supply%20Crate%20Key - average ~$2.45

10/2.45 = ~4 keys