It is difficult to value
I don't know how many 3 number combinations there are with the number 8 - my guess is 100
I know there is 1,000 number combinations between 100-999 and
I would say if its easy to remember, passes the sound test and comparable sites within the .com are using it, then start over $500
a number like 888 is obviously king, 808 is the next best - I would say those 2 NNN would be negotiated in the low $x,xxx.00 range