As stated, if you want a bottom fed system, it's all about the Reo.
If you want a genisis or just the cheapest option then I'd suggest the Smoktech Magneto and a Smoktech RSST genisis RBA. The whole set up, batteries and charger included, could cost you as little as $100. Didn't think about it when I bought it but they are conveniently from the same manufacturer...
Anyway, the Magneto and RSST will run about $80, probably with shipping if you look hard. I would suggest Steam Monkey if you want it fast and cheap. Shipping included they have the best price I found on the Magneto and the RSST is $33.
Batteries and charger are what really determine the over/under $100. If you're going sub ohm I would suggest the Sony US18650VTC3 30Amps. You can find them for between $7 and $18 depending on where, and when, you get them. FT currently has a 2 pack for $11.34, but be aware that you'll wait about a month for them to arrive. East Side Vapors has a decent deal on them right now too at $11 each. For the charger Pila is the big boy, but it's like $50. A Nitecore i2 is between $10 and $15 and will work just fine.
Can't really advise on anything else personally. This is the only mech setup that I own. Only other thing I can say is avoid the Sigelei #19 as there are a lot of problems associated such as reports of the button arcing and shocking your finger.
SmokTech Magneto
RSST RBA
Sony US18650VTC3 18650 1600mAh
http://www.amazon.com/Nitecore-i2-Intellicharge-Charger-Battery/dp/B0096U26QQ