Wow - 800 letters?! Lucky you...
My preference for something like that is a scanned signature and a good printer. :-)
But I know, that looks just so impersonal and is many times unavoidable.
My choice of pen: Pilot Rolling Ball V5 / V7
http://www.pilotpen.us/products/rollingball/Sometimes though, they end up leaking, especially after a few airplane trips. They seem to just ooze out the front.
Some of those space pens are supposed to be very durable, but not so inexpensive, and definitely not disposable.
It might be worth your investment to get a good refillable pen if you spend a lot of time writing. Although, then losing it could be a problem, and it might prompt you to get a pocket protector and... on the cycle goes.
Basically what I am saying is that I felt the need to respond and give some rambling of my opinion that barely makes sense to myself instead of just saying "I have no idea."
