Speaking of airlines - I've been meaning to ask this. I'm looking a taking a trip to the west coast and want to make at least one connection, maybe two. When booking online, can I choose different classes on the 2-3 planes? If so, at what point do they show the upcharge?
There are a few ways to accomplish what you're describing.
1. Book individual (unlinked) tickets each with their own class as desired.
2. Book a coach ticket and then upgrade one or more segments with a surcharge.
3. Book a coach ticket and then upgrade one or more segments with loyalty points.
4. Select a premium cabin during the initial search and then look for mixed class results.
5. Pay extra for a manual agent-created booking at an airport counter or by phone.
#1 has no extra surcharge. You simply pay whatever each ticket costs for each segment.
#2 and #3 can usually be done anytime between booking and check-in on the airline website.
#4 is best accomplished on an aggregate booking website rather than an individual airline website.
#5 is becoming more difficult over time as new agents are no longer taught special booking functions.
The specific options and methods vary by airline.
I do not think you can chose different classes on each direction. (Like economy on the 1st segment, First Class on the 2nd segment and Business Class on the 3rd segment, without pricing point to point.) it's either all or none. But some airlines allow you when redeeming a frequent flyer award to go coach one way and First Class the other.
Not only can it be done but sometimes it's impossible to avoid. For instance, buying an international first class ticket that connects to a domestic first or business-only regional flight or coach-only puddle jumper.