I think the easiest way to price them is to go to eBay, search on "78 rpm records", and then click on "completed listings". That way you can see what individual records have actually sold for. Aside from condition, individual records vary widely in price depending on what exactly they are. For example, a 78 rpm Johnny Cash record sold for $38 on eBay recently.
Condition is everything with records. If these have been stored in a non-climated-controlled area for years, they may be warped or scratched, in which case they will have little or no value. If they are in mint condition, then the research on eBay is worthwhile; you may have a few rare ones that are worth selling individually.