First of all, I'm sorry if here is not the right place to post this.
I have 1951 products in my webstore, and I need to upload prices for different groups of customers, doing it manually it's too hard.
Is there any way to upload product group prices by (.csv) without using any tool/extension?
Unfortunately, default Magento 1.x does not support import of group prices. It is possible to achieve with extension or custom code.