iTaste VV - not quite the shape of an eGo battery, but it's roughly equivalent. 800 mAh battery, variable voltage/variable wattage, ohm checker, battery life indicator, puff counter. Pass-through feature. Very affordable.
Vamo - a good mod. Easy to navigate/understand menu. Variable voltage/variable wattage, ohm checker, battery life indicator. Can be converted into "shorty" mode to make it smaller, sacrificing longer battery life. Only drawback: buttons won't lock. Also very affordable, although you will need either an 18650 or (possibly 2) 18350 batteries, as well as a battery charger. That will add to the cost.
iTaste MVP - also a good mod. Solid battery life (2600 mAh?). Will last you at least two days before needing to be recharged (on average). Variable voltage (3.0-5.0 volts), puff counter. That neat little rainbow of colors with Innokin buttons. Has an output function that will charge a cell-phone or other usb devices in a pinch. Somewhat affordable. Drawback: the MVP IS the battery, just like an eGo. If/when the battery dies, the whole device becomes useless.
iTaste SVD - (I swear I don't work for Innokin, I'm just thinking of decent, affordable mods for you) very solid, well-built mod. Telescoping, so it will take three different battery configurations. Variable voltage/variable wattage. Ohm checker, battery life indicator. THE BUTTONS LOCK! Unique design. Really looks like a lightsaber. Innokin button rainbow. Flawless ability to adapt to eGo threaded gear like iClear 16's, Kangers, eVods, etc. You will also need external batteries and a battery charger. Kinda affordable.
Seigeili (sp?) ZMax - 18650/18500 tube mod. Variable voltage, variable wattage. Very crisp, clear LED display screen. Menu takes a little getting used to. One button menu operation. Solidly built. Threads may not line-up with any and all 510 connections. No need for the buttons to lock since the device has one button, a la the Provari. May still be affordable... I got mine barely used for $50, charger and batteries included (the batteries included with the Segeilei Zmax kit -- the blue ones -- suck!! Toss them if you choose this route -- or maybe save them for an apocalypse emergency).
Lavatube/Lambo/Cylon, et al - Chinese variable voltage tube mod. Meh. They're still around but I think their hey-days are over. No ohm resistance check (that I am aware of). Battery life indicator. You will need an external 18650 battery and a battery charger. Not knocking these mods, but you could do better for the same amount of money.