I've been looking at some logo design companies, but have no idea if they are considered reputable or not.
They cost around 250-300$. I would name them, but I'm not sure if that goes against the forum rules or not.
Good logos can cost anywhere from $5 to $500,000 and probably more. The price does not necessarily equate to the quality of the finished logo (look at the 2012 London Olympics logo!).
Also, someone who has designed a great logo for a banking company might not be able to design a great logo for a community gardening organisation.
You need to approach the company and ask to see their portfolio (as with employing any design service). Ask them to talk you through their examples as case studies; get them to explain their working process and their rationale for making particular design choices.
The idea is to see if their approach to design fits with your business goals.
It really depends on what you want out of a logo. If you just want a nice graphic then many sources might be good. However there is more to consider when buying a logo.
In the end, a good Logo designer often needs to interview you and access your workers. Likewise, you as a company often need the logo designer to explain logo rationale and usage scenarios. Also, a logo quite often would mean changing the whole look and feel of the company collateral.
That process in general costs more then $300 in most locales, in just lost productivity of meetings, but not all companies are born equal.
To determine if these companies are reputable, I would suggest asking them for Case Studies and Client Testimonials. Ask if you can speak to any of their past clients for a reference.