Here is a buildlog video for a DIY 5.8G 200mW VTX including a 600TVL with 170deg FOV lens and a cloverleaf antenna under the constraints to be as cheap and of course as lightweight as possible. My solution costs 31USD and reaches 7.4g (you can probably be below 7g with better soldering job).
Pololu S7V8A Step Up/Step down (tuned to 4V) https://www.pololu.com/product/2118
1.25mm micro-JST 2p conectors (male+female) http://www.ebay.com/itm/20-Pair-Micro-JST-1-25-2-Pin-Male-and-Female-Connector-plug-with-Wires-Cables-HK-/291478049511?pt=LH_DefaultDomain_0&hash=item43dd7212e7
Total bill: 11.16+9.80+3.99+6USD + 3.94/20 = 31.15 USD
If you want to install a narrower lens, you need a M7xp0.5 compatible one, for example the 808#16 lens model: http://www.banggood.com/Lens-D-Module-120-Degree-with-case-for-808–16-HD-Camera-Camcorder-720P-Mini-DV-p-906428.html