I was browsing through one of our forum sponsors website , MGL Avionics, as I'm known to do from time to time, and came upon their antenna offerings. This looks like a pretty good price for a streamlined transponder antenna. They have good comm antennas too.
I'm looking for many different items now that I'm building again and this caught my attention.

Spend a little time cruising the sponsors sites. Lots of changes on some.

I found this under their "accessories" link:

http://www.mglavionics.com/html/accessories.html

DPA Transponder Antenna
Streamlined Transponder Antenna
Non-TSO’d for Experimental aircraft
The Delta Pop Aviation streamlined transponder Antennas are the best non-TSO’d antennas we have found, and they offer a low drag solution at a good price.

Frequency - 1030 to 1090 MHZ
VSWR - Less than 1.2:1 Measured with Anritsu Antenna Analyzer
Polarization - Vertical
Impedance - 50 Ohms
Connector - BNC Female
Mounting - 8-32 x .437” long threaded studs
Weight - 2.6 oz / 74 grams
Finish - White Polyurethane
Price: $69
Click Purchase to order today!