Writing is like modeling. There are many more scammers out there than reputable companies.
Rule #1. If they ask for money up front, they're a scam (or a vanity publisher, if you want to be nice about it). They're not publishing your book and selling it; they're taking your money. And printing a few hundred books and trying to sell them yourself is just silly. It isn't going to work, no matter what the "publisher" tells you.
Rule #2. Traditional publishers are dead or dying. You can still get work published by these houses, and you do so by querying them with a manuscript. Most queries get trashed or ignored, and a very few will get accepted. You might get a small advance, or you might simply get a cut of the proceeds. Only a fraction of these published books are successful, so even this doesn't guarantee you any significant income.
Rule #3. Self publishing is cheaper and easier than ever. You can publish Kindle books through Amazon for free, as well as print books through Amazon CreateSpace. Print On demand publishers, like Lightning Source International, allow you to deliver books to bookstores and customers for a nominal fee (less than $100 for set up). The key is that these publishers distribute your books through retailers - book stores, Amazon, Barnes and Noble, or other major websites - and you don't have to buy inventory.
The simplest way to get published is to write and edit your own manuscript. You can sell it as an Amazon Kindle book or through Amazon's CreateSpace without any upfront fees at all (even for ISBN numbers). If the book is successful, then you can purchase an ISBN and use a cheaper printer (like LSI) to maximize your distribution venues and profit potential.