I'm kind of a member of the plate community...as I think I've mentioned before. So I can give a little insight on the whole lighthouse-plate-collecting concept.
Some plate people (including me), won't purchase on eBay, except in bulk. First off, if the plate isn't older than 5 years, it can't be sold on eBay due to eBay policy. Secondly, the prices tend to be jacked up compared to the community rate, and shipping is exorbitant for what is, in essence, a sheet of metal.
Another thing...lighthouse plates are "specialty plates." They're quite rare in the collector's pool, as they aren't as widely distributed as the regular-issue plates, and the amount in the trading supply is very small. Thus, specialty plates can easily cost $50-100 or more. A lot of lighthouse plates are especially rare, or only issued to certain regions or people, etc., and most collectors, even those who specialise in a region, might not have one themselves.
Plate collecting's a fun hobby...but it's easy to get pulled into fast. I started out with the "plate from every state" thing as a cool thing to decorate my walls with, and now got kind of sucked into it. I have to be really careful - I get really out of hand sometimes, even with the passenger issues I collect.
Of course, there's always the screwdriver method...that's frowned upon, though.
I'd personally like to get a set of the Baymen's Hertiage plates on my car...it's worth $50 initial fee to me. Plus, since it's harder to figure out the lettering system on them (as opposed to the regular-issue VAA-00A, which you can figure out is brand-new when it graces every brand-new car you see), so maybe it'll avoid a little bit of the stigma that might arise from a brand-new plate on a 17-year-old BMW. Most times when I see that kind of situation, my instincts of "new driver" are correct. I know that some people stigmatise that, so even though it's true, I'd like to avoid the profiling.
Yes, I am paranoid. I know.