Only a fool thinks he must choose only one profitable channel.
I see no problem in choosing only one channel of marketing when you are brand new to marketing and have limited resources. Regardless of whether you choose PPC or SEO, as the place to start, you will have a learning curve and you must pay a good deal to learn either. Choosing one or the other to focus on as a first step is ok, just don’t get stuck on only one if you can help it.
You guys that say SEO is “free” are very misguided in my opinion. It is not free, not ever, at least not to me. It always costs something, and for me, it is very expensive because it requires one of my most valuable resources, my time. You might argue that it is cheap if you put a low value on your time, but “free”, that is just a lie that you tell yourself and others.
If you value your time highly, then SEO is the most expensive channel to start off with, as it will require quite a bit of time just to get the data you need for the first round of optimization. With PPC you can get to that first data insight in a fraction of the time. Sure it may require a bit more cash investment at first, but as soon as you reach break-even it no longer requires investment to continue to gain marketing insights. In fact, in some cases, you may be profitable from the very first day. That is almost never the case with SEO.
I do believe that SEO is a channel we should all pursue, but don’t base that decision on what you read in a forum, instead of test and let the data guide you. Why guess when you could know?
Personally, I would never consider investing in a major SEO campaign without first gathering data from a PPC campaign to test assumptions about the value of a keyword. Why take such a big gamble when there is no need?