"Multi-Currency ACBC" in the Community Question Library can handle this. You can download it from here and import it into your local question library, then add one or more copies of it to your survey:

https://sawtoothsoftware.com/resources/question-library/multi-currency-acbc
There are a lot of steps to it, but hopefully the instructions are clear enough. I can help answer any questions that remain.

If your new price field was just a tenth of the original price, you could just set the "calculate" setting to this:

calculate: function(originalPrice) {
return originalPrice / 10;
}

But what you are doing is a little more special. What you'll instead want to do is add this HTML to the level that should change the price if it appears:

<input type="hidden" class="multiCurrencyLevel" value="additionalBenefit"/>

Then the "calculate" setting could look something like this (assuming the new price is meant to be 50 more when this additional benefit applies):

calculate: function(originalPrice, properties) {
var newPrice = originalPrice / 10;
if (properties['additionalBenefit']) {
newPrice += 50;
}
return newPrice;
}

Have a look at this post,

This goes through how you can identify the summed pricing attribute and use it in other calculations. With a bit of work I think you can tweak it for your purposes

https://legacy.sawtoothsoftware.com/forum/23213/conditionally-display-acbc-summed-price-and-overt-discount?show=23213#q23213