Our Approvals App handles this:

A basic solution is to create the RFQ, without editing the lines.
Don't use the "Send by Email" button
But better use the chatter to send email to your supplier (Asking for price or available quantities etc...)

Once the supplier answer, you can edit and add the price into the RFQ that you can confirm by yourself.

Hi,

By default there is no option of Purchase Request in Odoo, the flow of purchase starts from the RFQ. For the Purchase requests there are few third party modules available in the apps store for free, you can have a look at those modules if you need it.

1. Purchase Request: Purchase Request

Thanks