Time to revisit the Hellfighter Ven?
Well, after the house is done anyway.
You can purchase the non rechargable batteries for around $10 each via the bay.
For cables, original Surefire cables for $20. Even if you only use the connectors they're a steal.
You can find the PP8444 chargers for under $100. This charger only works if the BB 2590 is charged when you purchase.
The smaller Sherpa 50 batteries as you stated hit or miss. The larger Sherpa will work, but for the price, not for me.
There's three version of the 2590 battery. 6.8 amp hr, 7.5 and a 8.5 or 9 amp hr battery. The Surefire cases sold hold two batteries side by side.