Well, fortunately for me, I got some SA/DL cels few years ago, for 'reasonable' prices. The prices weren't too high between 2005 / 2008... At that time, a 'normal' cel would cost $200-$500, depending the scene of course, usually with a printed background copy... those with original background were more expensive, and even more for the 'top' scenes (Dirk & Daphne together, or and ending scene by example...). Since a couple of years, prices go higher, and so too much for me!
Caution with the last ones I've seen on ebay : scenes don't match all the time : the sellers put characters from one scene, and background from an other one! I've also seen mismatch between the characters themselves! And most of the time, it's not the original hand paint background, but just a copy. Just try to find the scene in the original video game before buying the cel of course.
Otherwise, owning a Dragon's Lair or Space Ace cel is something unique... It's the only game you can have an original & historic part of it, and it's Don Bluth stuff, so it's also 'Art'
Now...Art & money...each of us has his own perception of the things...