The following circuit shows a simple circuit to charge a cap to e.g.100-200v. This is for a wild life camera.The main requirement is low quiescent current, less than mA, by the primary side, after the flash capacitor is charged because the circuit operated by battery. Is there a simple solution for oscillator driver, preferably based on transistor, to this problem? 

Consider using this:  "DC-DC Converter 3V-5V Output Step Up Step down Buck Boost 300V-1200V PSU Module"

https://www.ebay.com/itm/DC-DC-Converter-3V-5V-Output-Step-Up-Step-down-Buck-Boost-300V-1200V-PSU-Module/264035829269?_trkparms=aid%3D1110001%26algo%3DSPLICE.SIM%26ao%3D1%26asc%3D20131231084308%26meid%3D303593509b5d4479a35466a0cb15c884%26pid%3D100010%26rk%3D11%26rkt%3D12%26sd%3D174073965556%26itm%3D264035829269%26pmt%3D1%26noa%3D1%26pg%3D2047675&_trksid=p2047675.c100010.m2109

If one monitored the capacitor voltage so when it got charged the battery was switched off and back on when it got low the average current drain on the battery would be acceptable perhaps.  One could use JFETs and large (mega-ohm resistors) so the drain would be low on the capacitor. The converter would be switched on and off as it charged and recharged the capacitor; so the average current draw would be acceptable.

Someone who knows JFETs better than I would be helpful here.