Could you provide some more context on the customer experience you are trying to create? Each product and variant can only have one price, it wouldn't make a lot of sense for a product page to show one product with two different prices on it generally.
Are you trying to set prices for different customer groups or something along those lines? If you can share some more information for me I can see if we can work on a solution!
Thank you for the additional clarification @Steel-23! I understand now why you would want that option to be available.
Based on how the admin sets up pricing and variants, this would require you to add an additional variant for these products to add on the price of installation. Because the installation is a separate service that is being charged for, it isn't the same "product" as the item without installation. I do have the steps available though to add on additional variants for your products if you want to create a new variant option for installation fees. You can also export out your product list (please make sure to save an unedited backup copy!) and update the variants through CSV as well.
You can review the steps for adding variants to an existing product in my forum post here: Shopify Community: Create Variants.
Please let me know if you have any other questions you need help with.