If you don't have the money to promote your Youtube channel you could try promoting your Youtube channel through forums related to your Youtube channel.
Post good information on the forums and add a link to your Youtube channel in your forum signature.
You can also add signage to your car if you have one and everywhere you go you'll advertise your Youtube channel or wear a shirt with your Youtube channel on it.
It might cost a bit for those but it's a one time payment and you'll reap the advertising benefits for years to come.
Also on your Youtube videos make sure your video titles are clear and match what your videos are about and write a good description of your video with keywords related to your videos.
You can also start a twitter account and promote your Youtube channel through twitter posts.
You should also use good video thumbnails, and grab your viewers attention right away and make videos that will go viral and people will share your videos and your subscribers will go up without you doing much else.