It's not a "rough value" question, tho.

For example, valid answers for Delta would include:

• 1 cent/mile using Pay With Miles
• 1.5 cents/mile redeeming for a coach domestic US flight
• 2.5 cents/mile for a business class flight to somewhere warm

There's no shortcut to doing the hard work yourself. Figure out where you want to go and how many miles it would generally take to get you there vs. cash alternative.

(Some of the bloggers try to shortcut the process and tell you but it's meaningless unless you travel exactly like they do. Thus why so many people have BA Avios they can't use.)