How about a compiled Windows program, no GUI necessary. You drag an unencrypted wallet.dat file to the icon; otherwise it prompts you for the filename, exiting if given an blank filename. It reads the file, extracts the keypairs, spits out "wallet.txt" to the same directory, and closes. Wallet.txt contains one line per keypair in the wallet. Each line is simply: 1PublicAddressBlahBlah, 5PrivateKeyBlahBlah, F75E80AC... (the third item is the private key in hex format.) Needs to work with newer unencrypted wallets, including compressed keys.
How long will that take, how much will it cost, and do you sell all rights to the code (including source) along with the program?
I'm going to consider this reasonably sized and since it's the first it will be free. I've never worked with berkeley DB before so it might take an hour or two.
Yes, you get all rights to the program.
Edit: could you clarify: do you want wallet.txt in the same folder as the program, or same folder as the .dat?