If you are using Magento 2, I have a recommendation for you.

Magento 2 Customer Quotation Extension developed by LandOfCoder

Using this extension, you can not only help customer add quotation for virtual product but benefit from a lot of amazing features as listed below:

• Ajax add to quote
• Easy To Use Add to Quote
• Add Note/ Comment For Each Product
• Live Editor For Price
• Automate Request For Quote Process
• Make a Remarks For The Whole Quotation
• Easy to Check Quote Request Process
• Easily Enable / Disable Quotation Section For Each Product
• Enter custom prices per product
• Add or delete products from the quote request
• Display On HomePage, Search Page & Other Pages
• All Magento product types supported
• Supports responsive web design and works flawlessly together with Magento's Luma theme
• Internationalization & Localization
• Convert a quote request to order using the admin panel
• Quick Manager
• Customer Relationship Management (CRM)
• Create Quote In The Backend
• Send email notification to customer when the Quote is updated
• Add Tax for Quote
• Ease to show Total Quote Table
• Fast speed with Magento Block Caching

When purchasing this extension, you can have it freely installed on your website by our developer. For further information, please contact LandOfCoder via:

Website: https://landofcoder.com

Email: info@landofcoder.com

Facebook: https://www.facebook.com/LandOfCoder/

Hope this helps!