For cheap tips a button down is nice. I know this is weird but I look for 70's style shirts. They have the bigger cuffs and necks. And ill buy stick on jewelry or iron on bead stuff for arts & crafts and add a little for bling to the shirt, if needed. I never try and spend $40 on a shirt project! They like unique anyways!
Even your boots, if you have a real crappy pair of boots just spray paint them flat black and then gloss black. Always useful for cuts or dull old useful boots.
And never forget Gloves, honestly, they can't tell while riding. I use dollar store black winter gloves with the grippies.
Hair nets are cheap, for the pin I bought a $.50 pin off Ebay
with a horse on it running, I just pin it through my braid and into my net so it looks pro. :)