I've only been serious enough about this contesting stuff to buy contest-grade balsa for the last year or so, so I thought folks may want to hear my thoughts on the one vendor I've been doing business with.  (I would be doing business with Lone Star, but they died.  RIP, Loan Star).

National Balsa has an "Aero Light Bargain Grade Balsa" which has a very attractive price -- so that's what I've bought in my last two orders, and I think I have received enough product to draw a bead on what it really is.

On their website, National states "Aero Light Bargain Grade Balsa (Contest balsa) is still structurally sound. It will have more staining and discoloration than our standard Aero Light Balsa. This product is a better buy (25% less than regular Aero Light Balsa) for models that are going to be covered anyway."  They also state "Balsa wood that is in the 4-7 lb per cubic foot range.  Also known as contest balsa."

On the whole, I'm fairly well pleased with their Aero Light balsa.  It is not exactly what, or as entirely satisfactory as I was led to expect, but for the money I still think it's a good buy for me.  I suspect that as I get even more serious about this stuff I'll be getting pickier about the balsa that I buy (and spending more), but for now I'm happy.

Reading their statement about their bargain Aero Light Balsa, one would be led to believe that this stuff is entirely identical to their regular contest balsa, but with more staining.  I do not believe this is so.  In addition to some purely cosmetic discoloration, the wood also seems to either be really nice wood that's on the heavy end of the "contest balsa" spectrum (or sometimes slightly heavier), or wood that has some other flaws to it.  

The pieces that I have range from about 5.5 pound up to 7.3 pound balsa.  The heavier pieces tend to be beautiful clear-grained stuff.  The lighter pieces have flaws such as saw marks on the edges, small punky spots, small knots, and the advertised staining and discoloration.  I have two pieces that have seriously wavy grain that rules them out for anything that uses most of the sheet, like a fuselage side, but out of the two dozen or so sheets I've gotten from them only one is really seriously compromised -- I think that's pretty good for "bargain grade".

I suspect that rather than just selecting the wood for color, the "bargain grade" starts as blocks that weigh out to less than 7 pounds per cubic foot, but then don't make the cut into the "real" contest grade balsa for a great variety of reasons.  So, the heavier stuff is presumably there because it was on the heavy side of a block (and some lucky dog got some 5-pound), or because, regardless of weight, other flaws were noted that put it in the bargain bin.

The bottom line is that I like the stuff, but if I really, really need top notch wood I'll have to grasp my credit card firmly in a "big spender" grip and buy their "regular" stuff.

http://www.nationalbalsa.com/Aero_Light_Bargain_Grade_s/206.htm

Edit: Oh -- their maple motor mounts and their plywood is top notch.  Ditto their screws, but when you buy screws you get a separate package from MicroFasteners.  Both of my orders have been very well packed in a manner that could have taken significant mishandling in shipping without damaging the contents, and both orders came in a reasonable amount of time given that I had them shipped by "cheapest -- best way".

Personally, I'm very happy with AK Models balsa. Pretty good stuff and quite a bit less than National.

Stunt Hanger Hobby offers Tom Morris' "Contest Grade" balsa. And contest grade it is! 

I like buying from Vendors that are in the SH Vendor's Corner.

I try to keep my CL purchases in house if I can. I'll trade with CL Vendors first unless I really really have to go outside, even if it costs more money. Call it dedication, call it foolish.

Tom Morris contest grade balsa, and here's what I have to show for it.

My first real stunt design that I took serious. Stuka tank buster, 55" in span, 31.7 oz, so far, framed, covered, doped and a coat of primer, plus, some extra unneeded scale detail!

I expect a total finished weight of around 46 oz. Even at 50 oz, I'll be delighted for my first attempt.

Also used Tom Morris, CF pushrods, control horns, ball ends and magnets.

Tom Morris/Stunt Hanger Hobby, soup to nuts.

Find him fast, in the Vendor's Corner.

Tim,

Try this:  http://www.balsawoodinc.com/about

It's pretty good stuff and the prices are right.

They don't list contest wood -- do you ask him to sort it, or what?