Buy cheap lumber from Lowes/Home Depot:
4″ Strips of wood
Qty: 2 strips, cut to 31.5″ each. 6 strips total for the background.
2″ x8′ Strips of wood
Qty: 2 strips, 2 cut to 31.5″, the next 2 cut to the height of your sign (line them up, then make a pencil mark).
Paint the 1x2s white, and the 1x4s brown. I use cheap apple barrel paint.
Glue and nail the top and bottom frame edges to the panels.
Glue and nail the sides on, use a clamp if you can to hold all the panels as close together as possible.
Design your layout in illustrator/silhouette/cricut software.
Cut your layout out of vinyl, then put transfer tape over the vinyl.
Apply vinyl to wood, remove transfer tape. It takes a little finessing to keep the vinyl down, especially if your wood has lots of character.
Dab paint onto your wood sign through vinyl stencil, then remove vinyl. I do it while it’s still wet so the paint doesn’t crack.
Coat the sign with polyurethane. This is my biggest expense, and makes the sign look amazing. Don’t go cheap on this product. Buy the real thing. From my link, or from the hardware store. I don’t care, just get the real stuff.