As there are only 676 possible combinations (26 letter X 26 letters) L--L coms are rare!
But they aren't the most liquid (basically easy to sell cause of rarity) of short character domains!
Personally I would "promote" the rarity and try to sell them as a lot!
Low to Mid XXX per domain would be my estimate..
Your N--N (0--7.com) is even rarer 10 numbers (0-9) X 10 numbers (0-9) = 100 possible combinations.
Note I been trying to sell N--N for awhile now..no luck so just part of my long term portfolio