Delta Air Lines has always been very active selling and gifting SkyMiles in exchange for cash. They just sent an email blast and I was one of the recipients. According to the Terms and conditions the offer is targeted, but with Delta you can really never tell.
You can essentially buy SkyMiles for 1.1 cents per mile, when buying in the chunks of 30000 miles at a time. The fee per transaction is $30 and maximum number of miles transferred at a time 30000. Delta will give you back the number of miles you gift up to 150000 SkyMiles. Whether buying miles makes sense, is entirely dependent how you are using them.The best use of miles is for international business class tickets. This transfer offer probably doesn’t really benefit you if you are using miles mainly for domestic flights.