This post explains how to setup RFQ-ToolKit Plus to buy now or request a quote at checkout-based on type of products in the cart. If the cart contains a quote item, then customer can only request a quote at checkout. Prices for these quote items can be optionally hidden or remain visible. Items are marked as quote items in the advanced section of product setup.
Select RFQ and choose to show prices.
Step 2: Select option 5 & 5c to activate the rule.
With this setup, if the cart contains a quote item, customer can only submit the cart as a quote request.