I know exactly what you mean. I am INCREDIBLY broke. So broke that I had to cut my smoking budget down to $50 a month, by buying bulk tobacco and rolling it myself.
I couldn't afford to waste money. Whatever I got, I had to make it work for me, because I didn't have the financial ability to make mistakes.
I have now been vaping for 2 months, and I have spent about $150 total. And not all of that was strictly necessary.
I bought my kit for $35 (Kr808D-1), and it got me off cigarettes the first day.
I bought a DIY juice set-up for about $50, and I still have supplies from that original purchase to make juice with.
I got an extra battery, extra cartomizers, and a PCC (about $35 all togehter) to keep me going, and to charge my batteries when I'm out (a PCC is not necessary).
I have bought some juice here and there, but I haven't spent much more than $30 on it.
And I got involved on the PIF board, sending stuff to other people and them sending stuff to me, and not only do I feel like I'm doing something positive for this community, but I can continue to vape without spending a ton of money.
You CAN vape on a budget, you CAN make it work for you, and it IS worth it! Don't get discouraged.
For kits, the best starter models are the Kr808D-1 and the Joye 510.
I chose the Kr808D-1 because it has longer battery life, and a warmer, stronger throat hit. As a full-flavor (sometimes filterless) smoker, that was important to me. It is a 2-piece system with a battery and a cartomizer.
The 510, on the other hand, has better vapor production and the taste is "lighter" and cleaner. It is a 3-piece system with a battery, atomizer, and carts.
Either of these models will work well for you, and either one can be bought for under 50 bucks.
I bought my kit at ElectroNicStix and had a great experience. They also sell juice on the site. I have heard good things about the Boss juice.
Buy an extra battery or two, and extra cartomizers/atomizers and carts, and you're set to get started.
For nicotine levels, you will just have to experiment. Unfortunately it is hard to guess what will work for you, since it doesn't always correlate perfectly with how you smoked. I would recommend you buy small bottles in 12mg, 18mg, and 24mg, and try each. When you find the one that works for you, you can simply mix the others down.
For me, I go through about 60ml of juice in a month.
Please ask if you have more questions - there are ways to make this work for you.