What are the transportation options between the Miraflores locks visitor center and the Gamboa Rainforest resort? And how much would each usually cost?
The most common way would be taxi or Uber. Although, Uber can be pretty hit or miss and sometimes they don't bother to show. Taxi will probably charge $20 to $30, as the resort is about 20 km from the visitors' center. Taxis usually don't like to go there because they may have to wait a long time to get a fare back to town, or they'll have to deadhead back without a fare.
Another option is the bus. You would have to walk out to the road, or take a bus from the visitor's center to Albrook and another bus from the main terminal out to Gamboa. I'm not sure about the costs, but they would be cheaper than a taxi.
Bus from the locks to Albrook: 0.25 USD.
Bus from Albrook to Gamboa: unsure, and also don't know about how frequent they are. I do know that those buses depart from Exit 11 (Platforms 56-62) in Albrook Bus Terminal, and you'll need a RapidPass card to pay for the 0.10 USD a the turnstiles to get to the platforms. Those cards can be bought at the terminal in several kiosks.
It's quite a hassle to go there by bus, but doable.
In theory, you could walk out of the locks to the main road and wait for a Gamboa bus to come around the bus stop there, but I don't have enough info to know if you can expect buses to show up around frequently. I don't think there's a lot of demand for that route.