Out of curiosity, I decided to fire up the fight-o-matic and have the Skill 4 Mad Cat Mk. II 4 fight the Skill 0 Jump Infantry (Ballistic). This was using the 1v1, 10k repititions mode. The Mad Cat won every fight...all of them. No ties, no wins for the infantry. Mad cat 10,000 to nothing. So, for me that is enough to say a flat 50PV for Skill 0 is too much.
But why stop there!? I decided to give the infantry a more fair match, so I pulled up the stats for the Charger 1A1. It also has no damage outside of short range, and it moves 10" but doesn't jump. Also, it's only 18 PV. So, I left the infantry at Skill 0 and the Charger at Skill 4. The infantry managed to pull out a few wins and a couple of ties...and I do mean few. One round was 9987 Charger wins, 7 Infantry wins, and 6 ties. The other round was 9997 Charger wins, 1 Infantry wins, and 2 ties. So, in this case dropping the Skill on the infantry to 0 isn't even close to worth 11 PV!
What else can I try against these super-elite crunchies? How about something less beefy? Spider 10K it is! 17PV, 1/1/0 and only 3 health. It's fast, but damage and health are about as low as they can get and at skill 4, the infantry might have a chance. Well, they did have more of a chance, but still got stomped. Both fights ended up at around 6900 wins for the spider, 1300 wins for the infantry, and 1800 ties. So, even without the health advantage, the infantry at skill 0 aren't worth even 10PV.
So, lets go lower! Galleon GAL-100: 13PV at Skill 4, 2/1/0, 12" move, 4 health. Nope, still not enough. Galleon wins about 9700 times with about 200 ties and only 100 wins for the infantry. At this level, it's looking like lowering the skill of these infantry all the way to 0 isn't even worth 6PV! Fine, we go even lower.
How about we have them fight some other slightly-less-cheap infantry! How about the "AA Mechanized infantry Mechanized AA Infantry Point, 67th BattleMech Cluster, Iota Galaxy": 10PV, 1/1/0, 3 health, and 6"w move. Basically, they have one damage at medium and one extra health pip than the Skill 0 jump infantry. Is that enough to make Skill 0 a winner? Nope. 6500 wins for the AA Mech.Inf., 1900 ties, and about 1500 wins for the Skill 0 infantry. Well, now we have a slight problem, as making these infantry Skill 0 is worth less than 1 PV per decrease! These infantry suck so bad that there is no room for discrete steps between each skill decrease, even when fighting equally crappy units!
Thing is, this holds true for the vast majority of units that are under about 15 PV. Paying even 1PV per skill decrease is probably too expensive! Because of this alone, I'm willing to say, "no flat rate for skills. It must be somehow related to the PV or stats of the unit." I doubt I've changed your mind, since I don't think you see a reason why you would ever put a Skill 0 pilot in a 7PV unit, but hopefully you can see where I am coming from.