Ok, so I know what you're thinking. Stranges? Really? Are you really going to include a random part of the economy and not hats, vintages, or genuines? My answer:Yes
The reason I want to touch on this topic is because this subsection of the economy is always changing, especially when a new crate comes out. So first of all, let's talk about what stranges and strange parts are.
Well, stranges are simply weapons that track kills, or in certain instances a specific action. Take the razorback, which tracks backstabs prevented instead of kills. Makes since, a razorback that counts kills won't get to Hale's Own anytime soon. Strange parts simply add another modifier to that strange. For example, a Strange Part: Domination Kills will not only track normal kills, but track kills that have achieved a domination on a player.
Now that we know exactly what a strange is, let's talk about prices. When it comes to stranges, you've really got 5 categories. And hunker down too, this sections a biggy.
1. Crate #30 or #40 Stranges
When it comes to stranges, these are truly the diamond in the rough. These babies cost butt-loads more than the normal strange bat. Why? Because the crates 30 and 40 are salvaged crates, and only drop once every now and then. Stranges from 30 cost more than 40 generally, due to the fact that 30 no longer drops. At the time of writing, 40 still drops. Some examples of these stranges from salvaged crates are the Strange Huntsman, Strange Holy Mackeral, and Strange Kritzkreig.
2. Old crate stranges (#19 - #21, #28)
These three crates contain the most expensive 'common' stranges. The 19 has the grenade launcher, the 20 has the shotgun, and the 21 has the minigun. Now, you might ask what's with the 28? Every single strange in the 28 is worth at least 1.33 refined at time of writing. These crates cost a lot, but not as much as salvaged crates.
3. Run of the mill stranges
These stranges are very cheap, as the maximum strange from the recent crates might only catch a few keys. These are the least expensive stranges. Good for low income traders to test out the strange feature.
4. Strange Festives (oboi)
These hands down are the most expensive stranges. These only came from crates in the Christmas Event, and fetch a high dollar. The most expensive right now goes for (approximately) 2-2.5 buds. That's right. 2.5 freakin' buds. Never thought stranges could be so expensive eh?
Well, these are only obtained through MvM, and in my opinion are completely underpriced. These are stock weaponry with a chain and a bot head attached. There are 8 types, 4 of which are common and inexpensive(silver, rust, carbonado, and silver mk.II), the other 4 are more dollar-worthy(gold, blood, diamond, and gold mk.II). My reasoning is that you can pay for 6 MvM tickets (which are still overpriced at 3/8/13) and only get a strange silver botkiller sticky that only fetches 2 rec. And, you spend all that effort on Expert mode (which can take weeks to complete, if not months depending on skill), and you end up with a carbonado worth a ref. Really guys? This is how you value gameplay?
Also, on a different note, when a recent crate is released into the economy, the stranges inside are highly inflated, and cost a shiz ton. For example, you had to buy the Strange Baby Face's Blaster for 2 keys initially, and now it costs a rec.
Whew, that was a typefull. Big section, a lot to learn, but if you know how to capitalize on stranges you can make bank.