I'm assuming by "a few hundred rubles," you meant a few hundred "dollars" worth of rubles, right? Not to be a pain, but I just wanted to be sure you're aware of the exchange rate. A few hundred rubles could amount to less than 10$.
As for the quality of nesting dolls, I also don't want you to worry too much about it, as it's not worth it. Imagine if someone came to New York and said, I want to know the difference between the Empire State Building statuettes meant for tourists and the "real" statuettes. A New Yorker would probably laugh at that. There are cheap ones and expensive ones, but no one buys statuettes of buildings other than tourists, just like most modern Russian families don't buy nesting dolls for their kids any more ...they buy the same things you buy in Toys R Us. We're not talking about Faberge eggs here, that need to be certified real, or something like that. All of the nesting dolls you see in stalls around monasteries, churches, town centers, kremlins, museums, etc. will be there specifically for tourists. Whether they're made super fast and cheap, or with hours of careful painting work put in, they're there for tourists, not for modern Russian families, I assure you.
The thing you should really remember is that this means NONE of dolls you'll come across will be "fake." They are all, in fact, "real" nesting dolls in the traditional Slavic style - they just won't have been made 100 years ago. )) That having been said - the BEST way you can be sure it's worth your money is to just look and decide on the quality for yourself. You'll see a range of prices and designs anywhere you go, from small Donald Trump dolls to large ornate "traditional" khokhloma style (the red, black, gold flowery swirls) ones. If you decide you'd feel comfortable spending money on it, then it's "real" and "worth it." But you'll never get a certified nesting doll anywhere, as there is no such thing, as far as I'm aware, as an official nesting doll manufacturer, just as there's no such thing as an official NYC statuette manufacturer you should be telling your foreign friends about.
If price is the most important factor, lots of people here have given great tips on where to find good deals. The rule of thumb is always: the further away from the tourist center you go, the better the price will be. But the eternal follow-up question is: is it better to pay the extra $20 by the Kremlin and save yourself the hassle of searching, or is it better to save yourself the money and put in more boots-to-the-ground time?
Either way, I hope that puts your mind to rest a little. You'll have a great time and happy matryoshka hunting!!!! ))))))