5300cs:
Try going to
http://www.galaxyhp.com/memory_desk.html . I looked long and hard and they have a 64MB 5v 168-Pin EDO DIMM (aka, the memory used in the PM5500, 6500, TAM, etc) for only $33! This isn't the company I went through, but I don't remember who I did order mine from. But RAM is RAM for the most part, especially this older stuff. Plus, this site claims to have a lifetime guarentee, so that is even a better bonus. If that doesn't work, let me know and I'll help you find another store you can order through. Just scroll down the page to the "PowerMac 5400/6400, 20th Anniv. Mac" etc header. I am sure you are going to have to pay a lot on the shipping since you are overseas, but I bet you will save a considerable amount compared to buying it for over $100 in Japan. And what that one guy said about having to use laptop memory, he confused that with HDs. Yes, the TAM has to use laptop HDs, but it uses desktop RAM (although this was exceptionally expensive RAM for quite some time). Also, that myth of the TAM not working with drives over 4GB is just that: a myth. They had some problems apparently in the past, but since then, most people have had great results using anywhere from 12GB to 40GB HDs. These laptop HDs are more expensive than desktop HDs, I will say that much, though.
Also, your TAM should run OS9.1 just fine without the upgrade card, but the upgrade card will definately help make the system seem more responsive.
Now, to disprove that myth that a pre-G3 computer cannot run anything past MacOS 9.1. Well, I have a PM6500, and without any help from any articles or anything, I just used TomeRaider and installed OS9.2.2 manually. True, the system has to be the OS9.1 version, but everything else is 9.2.2. Also, there are numerous hacks that enable OSX booting on pre-G3 macs. I wouldn't really recomend it considering that the computer will run rather slow, but it can, and has been done many times.
Also, if anybody ever needs help with 5500/6500/TAM issues, IM me and I'll be happy to help out in any way possible. I have had enough experiance with the 55/6500 that I rattle off most of the specs for both of them off the top of my head (yes, that is a sad life I lead

), and the TAM is in many ways akin to the 55/6500 line, and I would be happy to look over some info I have on it if needed to help someone trouble-shoot anything.