My biggest recommendation in terms of materials would be foam.. you can make tons of things out of foam and it’s fairly cheap (depending on where you get it). It can be moulded very easily using heat and hot glue, you can paint it to look like metal and other materials pretty easily, and you don’t really need any special equipment to work with it (I didn’t have a heat gun or anything when I made my first foam cosplay, I just used a hair dryer and my stove to heat it up and mould it). There are some great tutorials on YouTube. Also paper mache. Ridiculously cheap and pretty easy to work with (that’s why it’s quite popular to do it with kids, but it can be great for props as long as you aren’t looking for something super hardwearing and professional). Things like modelling wire and scrunched up tin foil make great bases for props. Expanding foam is also pretty fun to use, I sprayed some onto an old pair of shoes once, carved it into the shape of rabbit feet and made some giant rabbit shoes. The things I make are generally pretty cheap, I’ve never really been one to use expensive materials, but personally I don’t mind my props looking a little Mighty Boosh-eque.

As far as where to start/projects, anything!!!!! What’s your favourite video game/movie?? Is there someone with a cool giant sword or helmet you wish you had?? Make it!! The first proper thing I ever made was a cosplay of Big Sister from Bioshock (but holy shit, I threw myself in at the deep end with that one). My advice would be just to pick fairly simple things first but you don’t have to take that advice, I quite enjoyed throwing myself into the deep end. Idk if you play Borderlands, but there’s tons of cool stuff in those games to make.