Newegg ha Rosewill RNX-A5-EX 2.4 GHz Indoor Omni-Directional (5 dBi x3) High Gain Antenna for $24.99 + free shipping.
Specifications Frequency Range: 2.4\2.5GHz
Gain(excluding cable loss): 5.0dBi
VSWR: 1.92 : 1 Max.
Polarization: Linear; Vertical
Radiation pattern: Omni-directional
Impedance: 50ohms
Connector: Reverse SMA Plug
Cable Loss: 2.1dB Max.
Cable Type: RG-174 Coaxial
Cable Length: 100CM
Operating Temp: -10ºC ~ + 60ºC
Upper Fixed Base: PU/PC
Bottom Fixed Base: PBT
Color: Black
Weight: 0.53lbs
Features
Features Low loss extended Cable allows versatile placement for optimal coverage
Compatible with Rosewill TridentX series N desktop adapter and router
2.4 GHz indoor high gain antenna Increase the performance for 3x3/ 2x3 802.11N device.
5 dBi Omni directional antenna with magnetic base
SMA connector. NOT for TNC interface device.
Rosewill RNX-A5-EX 2.4 GHz Indoor Omni-Directional High Gain Antenna $24.99 FS 
