What do you mean by expensive traffic?
There are various strategies that you can use to increase traffic on YouTube.
The most effective way is to promote your videos and engage with other users through comments, likes, and shares.
Another good way is to participate in the communities of similar content creators who have a large number of subscribers or views on their channels.
You can also find other bloggers who are popular for writing quality content and ask them if they would like to be featured on your channel.
You can also post sponsored videos that contain some sort of advertisement in it so that viewers will not get distracted by any ads while watching your video.
In addition, you can use an online service like TubeBuddy or VidIQ which will help you track the performance of your video from all angles such as views, click-throughs, subscribers, etc. They will help you optimize your content so that you get higher rank.
However, the fastest way to grow your channel non-organically is promoting through youtube ads. Otherwise, you won't have chance to rank high quickly especially if your niche is a very competitive one.
But, if your niche has low competition, don't worry, you have a very high chance of ranking No.1. Be sure to write content based on your keyword in the description box.