Forget the provari if you can't afford it.
I take it you're looking for a vv mod. A lot of people are geting the Vamo, also called the eGo APV (although its not Ego at all). I have one.
You can get one from $40-$60. Goes from 3-6 volts and is accurate.
You can also switch to variable power (variable watts) on the same device. Goes from 3-15 watts. Or just use it with vv if you prefer.
Comes with a removable centre extension - so you can use it 1x 18350, 1x 18650, or 2x 18350.
US vendor has them here, is selling out fast:
https://vaporbank.com/shop/index.php?p=product&id=884
Health Cabin have them here. I got one from there - they gave me DHL shipping cheap. Reached me in 3 days.
eGo Variable Volt/Watt APV V2 (Only Body) [D-B4 APV] - $39.00 : Healthcabin Electronic Cigarettes - Wholesale and Retail
Another vv device under $150 is the Zmax. Takes 1x 18650 or 2x 18350. Mad Vapes have them for $90:
Smoktech Zmax Variable Volt APV
The Zmax is variable voltage, and also has the variable wattage option. Is accurate.
Here's some pics of both pvs for you:
Vamo using 1x 18350 next to Zmax 1x 18650:
L-R: Vamo, Zmax
Vamo and Zmax both with 1x 18650:
L-R: Zmax, Vamo
I have both of these. Both have variable voltage, variable power, resistance check, LED on/off and other features. At around $40 or so the Vamo is a very good price.