Ozmo is right that they are usually a bit heavier than a Balsa counter part, but will win hands down in durability and ease of construction and reconstruction. If you built a Spadet to plans it will be about 5.5 to 6lbs. Which is just fine for a 40/46 size engine. The Spadet is a copy of the LT 40 Kadet which is probably a little lighter. You can usually build a SPAD in the same time it takes you to assemble an ARF. Talk to your local sign shops for Coroplast. Usually around 15 bucks a 4X8 sheet. you need a set of plans, 2mm and 4mm coro, some hardware from an old deceased ARF, some glue, hold your tongue just right...and presto! New Plane! Usual cost of putting together a SPAD is 20 bucks if you reuse existing hardware that you have. Oops! almost forgot. Some PVC down spout as well, if you can find the right stuff. It's the square stuff with smooth sides no ribs. You are looking for 2 1/2 X 2 1/2 that you usually find at the True Value/ Ace stores. They typically don't have it at the big boxers. You don't have to have the PVC, but the coro is a must have or it's hard to build a Coro airplane. While your at the hardware store grab some yardsticks. Need them for the spar!
They are fun to build and fly and you can use the skills to fix Balsa planes. A buddy has a Alpha 60 which he tried to hanger under someones car. So it needed a new wing. Fuse was cracked, but easily fixable. It would of taken me a long time to rebuild the Balsa wing plus covering H9 wanted a 120 bucks for a wing! So I made a new coro wing in about 2 hours and she flies great! The wing is about a half a pound heavier than the original, but works like a charm.

SPAD's are a little heavier and not as pretty as a Balsa bird, but are just as fun to fly! Fun! that's the whole point of this exercise isn't it?