Wardrobe depends upon your story. I suspect most big wardrobe decisions are made at the script stage. No money to do a WW2 film because you need all the uniforms, that ones out. No money to do a historical pagent because of all of the clothes required, out. If you do a movie about a few modern folks that talk or get killed and you have a much easier wardrobe issue to confront.

From that point you're talking about, (i) what clothes does the script say a character wears (ii) If the script does not say, what do clothes say that help present the character and help distinguish them from others (iii) do you need multiple versions of the clothes, depending upon the shooting schedule and blood or rips that might damage them (iv) Do the clothes have icons and logos that might require permission or have to be created from scratch.

In a lot of low budget movies (non student films) the actors might provide their own clothes (with some guidance) or get a small stipend to spend on clothes rather than have a proper wardrobe department. This is cheap, and that is one of the defining factors of low budget.

RJSchwarz

The problem I see with a lot of low budget movies (well zombie movies actually) is the production seems to have custom designed shirts. Probably online. These are fairly cheap and usually unique and funny and distinctive. All positive things. The problem is that they all look clean and crisp and unworn. Rub that new shirt through the dirt. Wash it with other colors. Leave it in the sun to fade. Force it to look a bit worn. Either that or get it long enough in advance to allow for some proper wear and tear.

RJSchwarz

For low-budget SF films, as I understand it, the actors have to bring their own.

I agree that wardrobe can be tricky and expensive, but I also think that if done right it can add a whole new demention to the story, allowing the script to be trimmed further. A character's development, for instance, can be visually shown through clothing. With the right resourses one could find considerable wardrobe options for their film.Used clothing stores offer a great selection of already distressed clothes.
The option of giving your actors a description of what is needed for wardrobe and letting them bring their own is a method that is used in many productions. However, it does have its fallbacks. For a period of time I worked background and was instructed on what clothing to bring for whatever roll they needed me to fill. However not everyone will be able to suppy the clothing that has been invisioned, so there was always a wardrobe van available to suppliment.
Creativity can be the key to a wardrobe situation. Adjusting filming scheduals to make for easier continuity, and utilizing every option to minimize costs can allow even a student production to have a more professional looking wardrobe.
After all don't we respond to the world visually? Our first impressions of a person is usually based on their physical looks. What a person is wearing, how they carry themselves, whether they are neat or frumpy, tells us things about their personality at first glance. We form a mental image of who that person is, right or wrong, and we respond to that person based on our own mental image of them. This aspect of human nature is one that can be easily exploited.

Nizbith

definition of failure: when one ceases to try or learn.

I'm joining you on hating too shiny and new costumes. I'm all for breaking stuff down, sitting there with a razor picking holes in jumpers and rubbing through the knees on jeans.

My current project is a post-outbreak zombie movie. These characters have been living rough and trying to survive for six months - they're not gonna look that great.

My plan is to go to charity shops and ask them for the stuff that's been donated that they think is too worn and old to sell on. Hopefully that ought to give me the look I need.