Welcome along, to the game and the forums 
Now, there are a good few useful sources and discussions that might be worth a look, which you can have a flick through (below).
The starting point for a lot of LARPkit can easily be charity shops and online second hand stuff.
Basic soft kit* for almost any nation can be the same: shirt, plain trousers, sturdy walking boots. This can be accessorised and altered for various nations.
Wintermark and Imperial Orcs CAN be fairly close in terms of basic clothes. I’d suggest hunting through charity or costume shops for the basics above (except for the boots. Get good boots. Suggestions available on request). You may also want to join your Nation Facebook groups, and ask if anyone has spare soft kit.
If you want to make this sort of stuff from scratch, I know some folk with some simple and effective sewing patterns, if you’re able to make stuff at the sewing machine level.
In terms of national tweaks, Orcs require a mask, which is probably easiest bought on site, although I can find the vendors if you want to get it first. They also may want a warskirt, which is fairly easily made from scrap leather (or similar enough); various bits tied to a belt, maybe decorated, and so on.
Kallevesi… luckily a lot of crow like stuff can be sourced from the goths and similar 
, but in extremis I’ve seen some good results from taking loose feathers of crow etc and sewing them on to fabric, or glueing them in with another band of fabric. They can also do well with simple mantles and capes with Wintermark runes painted on.
Armour (if needed) is a different set of questions, accessories can be sorted a little later, and weapons are best bought at the event (or, given the time till next major event, at a trade fair).
It is entirely possible to get a lot of reasonable kit for those nations on a small budget (with the possible exception of the orc mask). What sort of budget are you looking at, what sort of characters were you planning?
I and others on here can give a lot of advice on this, and will happily do so
*Soft kit is the fabric stuff, hard kit is the armour.
(And the facebook group for new player enquiries and discussions)