GLB is obviously waaaaaay too cheap if people find GM at $499 (or $449 on special offer) worth the asking price.
Not everyone can afford to own UR3, I am one of the few that do. Because of the royalty fees, it's not the most used product at the studio, but it has its few releases. Why I mention this, is to portray a standpoint from a different perspective.
I would not think twice about forking out a few thousand for a really really good c++ engine, simply because of its extensibility and speed.
However when it comes GLBasic, I would think 20 times, if I wish to even look at the product, if it were in the $499 bracket.
It is not because of the product itself, but because of the historical "slowness" stigma attached to the Basic language. Now that I - through personal experience - find GLBasic to be superior to many other c++ engines out there, I would easily throw a $200 - $300 that way. Why not $499 ? Well because engines such as Oddity3D, a new upcoming c++ engine has 50 times the power and although dedicated to DX11, it is in the $499 price bracket. It's all a matter of the tool, it's purpose, and ultimately the user.
I would however write an OGL particle system, and "bribe/donate" with $1000 to have it made as a part of the GLB core - simply for my own ego, if no other reason.
It's all a matter of perspective from the user's side.
PS: GM is (IMO) a plastic toy, and not a real engine. Sure it can make games; but so can Flash.