There is a guy on flea-bay offering 1930s era charts for 175 quid but if you look at completed listing they seem to go for around 20-30. Yours are, of course, considerably older so may be worth more. You could try and identify the ship they were used on. If they are associated with a noteworthy voyage it could enhance their value. Get you local auction room to value them or look online for a valuation service, I had a painting valued recently and it was a resonable price. Most auction rooms do free valuations in and around their local area, check the local paper, they usually list them there.
You could also take the precaution of storing the charts in acid free tissue which is much better for paper items. HTH