set Regular price by one of the attribute

Markup-by-Attribute can’t do that for you. At least, not as described. The problem is that Markup-by-Attribute does not adjust the base price of a variable product. You mention the 10% markup, so I assume you’ve figured out that marking up for larger quantities won’t work because the 10% will always be calculated on the base price. For instance;

Base price is $150
300 quantity adds $150
one attribute adds 10%
price should be US $330, but will instead be US $315

Fixed priced markups, like adding $2 for an option, won’t extrapolate over the quantity, either.

The only way around this (with Markup-by-Attribute, anyway) is to have each size as a different product, so you can set different base prices. That doesn’t address the issue with the fixed price markups, but percentage markups will be calculated properly. If you have “Related Products” on your product page, the different bulk sizes should appear there.

Sorry if this isn’t much help. Different bulk packaging options have been a thorn in my side for a while, and I’m still not able to find an effective way around it.

It is adjusting the base price of each variation and adding the variation description.
my pricing is too complicated, I am already making sizes as a different product, but I want to add quantities in one size.

If I manually add just the base price on each variation, the plug-in does not work, I have to do it through the option above that says set regular price.
It only works with a set regular price, does not work if I add the regular price manually.

maybe I can give you a solution for that, when we click set regular price, you can add a filter there that asks you to select one attribute to set regular price for that attribute. that is how it will be possible to set different base prices.

Also in the variation description, there is an error, it shows product Price $$150 instead of $150, it shows two $ signs.

It sounds like your pricing model is too complex for Markup-by-Attribute.

Much of the appeal of the plugin is that it is straightforward; it does one thing without trying to fill everybody’s needs. I want to avoid adding complexity to the plugin that may confuse existing users. And, since Markup-by-Attribute is a hobby for me, I intend to keep its scope limited to those things I can support in my spare time.

That said, I am working on a ‘bulk pricing’ capability that may fit your needs. It simply divides the base price down to a unit price, then multiplies the unit price times the quantity the option represents before applying any markups or discounts. I have no idea, right now, how long it will be before that is ready.

(The double currency symbol problem has been resolved in version 3.10.5. But, you will have to reprice those products with ‘$$’ to fix the descriptions.)