Are there two-way encryption algorithms that include a work factor?
You can use bcrypt to derive a (long enough) key from your initial secret value, and then use the key for symmetric encryption. "Guessing" the key is an issue only when the key is part of a space of possible keys which is small enough that such guessing is a possibility -- i.e. when the "secret value" is a password. A 128-bit uniformly random key is immune to guessing by virtue of being part of a space of size $2^{128}$. So use bcrypt with your work factor, truncate the result to 128 bits, use AES, and you're done: any guessing will have to work with the password, and will thus greatly suffer from the bcrypt work factor.