I just acquired a Kyosho Seawind that came without a mast or sails, but it appears to have rigging, the servos and receiver, etc. I have sailed full-size keelboats but I'm new to RC stuff. I am also on an extreme budget, but I thought it might be a fun thing to do with my boys. Are there any resources for inexpensive (ie, noncompetition) parts, or DIY guides, that someone could point me to? I have already discovered some 3D printable parts (it is missing the central hatch cover and the cover for the rudder yoke or whatever it's called) so I can take care of those, but I'm a little lost about what to do about a mast and sails on a budget.

Any help is appreciated!

Masts and booms are easy, wood dowels or carbon fiber rods or tubes. You can make the mast and boom fittings using a 3D printer or, if you have one, a mini mill using plastic or aluminum.
I might have gotten lucky. I found these just playing around:
Search results for: 'seawind parts' - KYOSHO RC
P01_SEAWINDout
P01_SEAWINDout
P01_SEAWIND KT-431S_out

Send me your email address and I will send you Seawind helps.
I am [email protected]