You can have a predefined price list just for a specific client. To create a price list, go to Contacts > Companies and find the company you need from the list or click on the "+" sign to add a new company.

When you select a company, click on the tab Price list.

Click on Create a price to add custom prices for this specific client. 

Next time when you'll be creating a budget, you'll be able to add prices from this list by clicking on Add From Price List 

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