For comparison, here's a 1903 proof 50 centavos that I bought uncertified a couple years ago and had graded by PCGS...
Looks like a proof to me. I think the PR-61 grade is about accurate. Don't expect a mirror/frosted effect on early Philippines proofs.
Not even close. Those slabs do have a small collector following, but they don't add anywhere near that type of premium. Especially when they have World coins in them. If it were a an average Morgan Dollar that sells for $80 or so normally, you might get $90-$100 for one in this type of holder if one of the PCCI holder collectors likes it. I've bought and sold probably 50 of these holders in the last 5 years or so.
illini420, has more experience here, go with his suggestion, my 150 estimate came from an older website, yet there they stated that these holders were scarce, very few around, there are some slightly similar holders made later which are more abundant. Perhaps illini420 could explain the differences. To me this is a very rare slab, until I receive more sure data. On the safe side, buy the coin, and yes I do not see the brilliance shown by illini420 's example, (his example shows a coin which has abundant hairlines, in the fields, I wonder, has it been polished?) but it, the coin you are interested in, still appears proof to me. As I said even if it is just a MS 67-68, great coin. (and INDEED, you did alert a potential buyer to this coin, one who buys low and sells awfully high!)