If you aren't advertising you're not going to get customers, let alone satisfied ones. Advertising on high profile/traffic websites will be cost effective if your product is good enough. I mean tm advertise on the same bunch of sites month in month out so it must be working for them.
You could take the route of word of mouth, referals and what not, but if you want to compete with the big boys you're going to have to go down that route sooner or later.