Orders and Quotes Tables - Database Design
How about combine them? Keep the idea of an order table as the base, and add a status field with values:


Entered - data being typed in, just started
Quoted - quote provided to customer
Ordered - customer has accepted the quote and the quote converted to an order


You mentioned keeping the original which is doable if you have an ORDERS_HISTORY or ORDERS_VERSION table. Basically, whenever the status of an order changes, update the main table but keep a snapshot of what it used to look like in the history table. This would let you pull up old versions of the quote/order to quote against.