The last time I saw Power Blade on ebay I bid $160.00, I didn't snipe and I got outbid with a day to go. I think it sold well north of $200.00.
Power Blade is one of the rare PC-10 games. NG2 pops up from time to time, still not terribly common. I would say it is more rare then Mega Man 3 but not as rare as Power Blade.
The rarest games and this is based on my own observation, not any quantifiable data would be these in decending order or rarity. I am sure I am missing a few in there but, I have never seen a NG3 for sale and only know of 1 KLOVer with one. I have never seen an RBI Baeball. I have only ever seen 1 or two of the next 4 for sale, and the last 4 maybe 3-5 for sale via ebay or KLOV in the last 6-12 months.
Ninja Gaiden 3
RBI Baseball
Solar Jetman
Rocking Kats
Power Blade
Shatterhand
Yo Noid!
Ninja Gaiden 2
Captain Skyhawk
Megaman 3