Floor price is around $50 these days for worst number combos, and it can go up to a couple of thousands, depending how many repeating numbers are there, if there are any premium repeating numbers, triple (quadruple) starting or ending repeating etc...lots of variables.
6n domains, if it's not contains o or 4, can get you really decent money. You can search sales history at Namebio.com.
If it has an 8 in it, the value increases, the more 8's the more domain is worth. Goldmines are domains with pattern (like 223344, 123321 etc) containing 8