Hi,
I live in Australia, so I can't help you with board prices in the US. I have been to California and Board prices seemed cheap compared to OZ.
Where are you traveling from?
You will have to pay airline excess luggage fees, depending in airline, either per board or per boardbag and it can get quite expensive (but worth it if you are going for longer).
Where you start your trip is up to you and also the time of the year.
I did multiple trips to just 1-2 countries in Central America but I also 1 trip from Panama all the way to Mexico overland. If you do that, then the dry season (Nov-April) is probably the best time to travel. June-Sept brings bigger swells but it's really hard to get around in some places. However, that's also when Puerto Escondido is best. I saw more broken boards there than anywhere and you will also need completely different boards than anywhere else to surf that. So you need to sit down and may your trip, see which countries you want visit and check surf season/monsoon. You might also like a place and hang around for 1-2 months because you get attached to a particular wave. So not enough information to really help. More research. I took 3 boards, spent 5 months on the long trip and left with none, all snapped and repaired multiple times and then given to local kids before leaving for good karma

You could also overland the whole lot and cross over the border from California into Baja and then make your way down and end up in Panama, depending on your time frame..... No airline board charges that way and the 1st class buses are pretty good and stop everywhere.