Yeah, it's pretty expensive to try and get really sizeable samples of the platinum group metals. Of all the money spent on my collection, the PGMs have basically taken up the most of that money. Thankfully I was able to get a really sizeable sample of Rhodium metal prior to its sudden spike in price. (I purchased my button when Rh was at about $800 an ounce, and right now it's about $3,000 an ounce!). With the PGMs, what I've done for the expensive ones is just purchased small amounts at a time, then eventually "trading up". I've been very fortunate to have done some trade ups with some of the element dealers I frequently purchase from as they've taken my multiple buttons of a metal and traded me an equal-in-mass larger button. I still need to get some more Osmium so I can get a troy ounce button similar to my iridium button, but that's going to take some time.
What I've found is that once you get the bulk of your collection done, you can then start to really specialize and try and upgrade the samples you have. For a long time, I had some sodium metal but no 'unoxidized' sodium. I then found a dealer who sold pure sodium metal in an unoxidized form sealed in a glass ampoule under argon. Now I have a nice sample of sodium. I hope to do that soon with my potassium metal as well. (Though right now I need to get a picture of my potassium. On one corner of my block, there was some freshly exposed metal surface which has oxidized in an unusuall manner. Right now, it has a deep, blood-red color to it with a pearlescent shine. This doesn't look anything like the peroxide/superoxide that I have read about, so I'd like to get some opinions on what it could possibly be. Right now, it's just really impressive looking).
For the gases, I'll also agree that having a vial of a clear gas is pretty useless. The discharge tubes are great for holding samples of the gases as you can run a small current through them and see the spectrum of that gas. For oxygen, I try not to discharge it too often as the high voltage results in formation of ozone gas out of the O2 gas and that will corrode the ampoule after some time.