Don't buy anything fancy just so that NVG's can see you - any red or white light is visible many miles away. We fly with NVG's and regularly see other aircraft's red anticollision lights over 100 miles away. Note that they can't see blue or green, though.
As mentioned dye markers are very visible; the trouble is the deployment time; they take several minutes to deploy and by then the aircraft has already passed you by. Smoke is the best. SOLAS approved is far better than USCG approved and worth the extra money
. Military surplus is great if you can find it.
Don't forget the EPIRB! That's the best money
you can spend.