[larrynjr]

I'm not sure on how to give it an antique finish, acid bath / vinegar maybe?

As for charging, I would certainly charge something, cost of materials plus a reasonable hourly rate. If there are other items you normally make that would be of an equivelent size / shape and you have a "normal" or know how long it takes to make that item I'd charge the shop rate for that.

When I worked computer / network support for other businesses and took longer to fix something then I thought it should take, I'd charge the number of hours it should have taken. Or if I had to do research to fix it and it was a general software issue (could or might happen at any type of business, not particular to theirs or their specialty software) I would charge a fair rate.
If you plan to never make another sword you might charge more for specialty work but if you think you'll do more swords in the future. Charge a reasonable amount that covers costs and normal forging time.