Your prices are too low.
Yes, probably, I just up all of them to 79... I just want try, I think when I get some sells I will increase more... Thanks for your opinon 
Yes i think 79 for avarage 4K clips would be fine, I use similar prices. But your better and more interesting ones and topics without big oversupply could go even higher than that. So i think 79 should be the minimum for 4K, and the avarage is somewhat higher.
As for supplying free clips... if your intention is to drive traffic to your portfolio i don't think it would work very well. Most of my experience is from the photo side, but I've found that it's very rare that people look into portfolios. Maybe if they find some really rare and special subject.
Some time ago Shutterstock used to have a counter for portfolio visits. That time I used to have around 100 sales/day and less than one portfolio visit daily.
But still, it happens once in a while that someone seemingly searches my portfolio and buys 5-10-20 images of the same topic. Still it's not sure that those are portfolio visits... maybe someone just buys hundreds of images of a particular subject and many of them happens to be mine just by luck.
I wouldn't suggest to give away free footage for anyone. A good footage clip really takes work in setup, processing, computer power etc.... It's not something that should be offer for free. In the past sometimes I gave permission to some sites to put one of my images as weekly free photo on their front page when they asked.
But i think giving free videos are not something to consider