9 foot wide roll of white backdrop paper, you can easily rig a system to hold it up off the ceiling with PVC and wire.
The next part won't be cheap:
You could get away with shooting cheap speedlights, but you won't have the option to use big light modifiers. Get a strobe and a really large softbox, if you figure out how to use it well it will take care of the majority of the situations you will get into shooting clothing.
A speedlight that you can fire straight at your backdrop will drop it out to total white as well, which is useful... but a second strobe would work better and be easier to balance power and color with.
Alienbees are cheap and have enough power to strobe in daylight for fill as well.
You can use optical triggering in a studio setup using the on camera pop up flash, it's crude but if you're trying to keep it cheap that's a small corner you can cut. It would be better to get a remote system - if you're not shooting action the cheap cactus ones or yuongno triggers will work fine, since you don't need them to work perfectly every time. The Paul C. Buff ones work better and are all you'll need for shooting just about anything, pretty reasonably priced.
Also, invest in a lint roller. That stuff shows up big time.