This is a good question, I don't know. What would an average system cost? 400, 600? I don't have to buy everything at once so if it is a little more I can piece it together. This is one aspect of photography I don't know too much about.
Don't mean to be rude but I just took a look at your signature and all I can do is shake my head. Color me with envy! Forgive me, but I'm going to assume you can afford more than a couple speedlites and knock-off triggers
. Although, granted you're as unfamiliar with flash as you said, it probably wouldn't hurt to be sensible and start out with a budget system so that you can learn the fundamentals and get a taste for off camera flash before you dive into a system of studio lights, grips and modifiers!
I'm fairly new to small flash and studio lighting myself but would like to think that my learning curve has been dramatically accelerated/influenced by my friends (pro photogs) and so many of the members right here on the forum. I'd honestly recommend starting out with a couple YN-560's and some RF-603's. Looking back though, one thing I wouldn't cheese out on if I could do it again is the equipment you use to mount your lights. Whether you start out with speedlites or some heavy monolights, spend the money and get yourself some decent light stands. Just like building a race car, you don't drop a 1000HP motor into a chassis with a weak transmission and flimsy suspension.
As for light modifiers, A convertible umbrella is always a good place to start! Not only can you shoot-through to diffuse the light, you can also throw the black cover on and bounce the light out of the umbrella. After shooting with and without a light modifier you'll learn very quick the difference in the quality of light whether shooting bare light, diffused and/or bouncing the light.
One thing you should know about the YN-560 is that it can throw just as much light as Canon's 580EX II although it does NOT include eTTL. For me personally, this doesn't matter at all because 99% of the time I'm using my flash in Manual. Lots to consider but don't be afraid to ask! 



