Getting to Salinas from Guayaquil doesn’t take that long… maybe 2.5 hours so depending on what time you arrive you should be able to get there easily enough. You can take a bus, but yes, I don’t think the buses leave from the airport. You could also rent a car, if you like, and/or hire a driver to take you to Salinas ($60-$100). One English-speaking driver you might try is Will Rodriguez: willienavy70@gmail.com; cell: 098-699-2334. A friend recommends him, I have not tried him myself.
Let me see if I can find more info for you.