Yeah, I definitely do not track postage, but I could see myself doing that. I used an Excel spreadsheet and I had to go through each completed trade one by one to add the amounts. I started by copying and pasting the completed list over to Excel to creat the list of trades by transaction ID and then went back in with a Sent and Received column to determine how many cards went out and how many came back. I had been keeping a separate spreadsheet with all the members I traded with over the years to keep track of addresses in case I had to resend something or maybe I wanted to do a PIF if the member sent me some extras. I had a few others ask me for addresses for just that reason (PIF) also. I don't give out addresses regularly, only a couple of times and only to well established and respected folks here on TCDB.
On the postage side, I use PayPal and print my own postage because it is cheaper than using the USPS. I also avoid going to the PO as much as possible and simply put the outgoing in my own mailbox and put the flag up. I use PWE as often as I can which is for cards about 20 or less in a #10 envelope between cereal boxes inside cut or folded binder sheets. I don't mind paying $2-4 each package of cards greater than 20 or for cards with patches inside bubble mailers because I would pay that for a pack of cards at the store anyways. This way, I know I'm not getting duplicates and I'm definitely getting cards I want and getting rid of cards I don't want and helping someone who does want them. Win win all around. The post office has to make money somehow and for $0.55, to send a couple cards across the nation, not too bad still.