It's true! Non member den betas are worth more in value as opposed to member dbs thanks to its availability (as a main reason to its popularity among players) as well as they're a little bit harder to get
Black longs go commonly for 30-35 as a base value. (As highlighted below on its page) Now as far as non member den betas are concerned, I'd say around to 20 dbs as long as all den betas included are non member, as a matter of fact. I'd advise to go either one way or another, as mixed dbs can be a little tricky when determining in total and assessing can be difficult to wrap your head around. Was that any helpful?