Very niche market but you can get modernised gramophones that sync with iPods etc now so certainly not a dead product. Might fetch mid to high $xxx but you could be waiting a long time for an offer to come along. Maybe one to develop and then sell . . .
My estimation is low xxx USD to mid xxx USD, but can be even more to the right buyer who likes the name (but like said above I think is not so easy to sell it).