Make them buy their own boots. Black Boots or Duty Shoes.
Get a Duty Belt and Belt Keepers
Issue them gear for their belts; Flashlight (or at least an O-Ring if your dept has a Maglight pool), Flash light Holster (Will vary by light), Pouch for rubber gloves, Radio Holster, Singular Cuff Case, and a pair of cuffs.
I suggest pooling different sized Duty Belts, they can pick them up when they go on ride alongs or do events. So you don't have to buy each explorer their own. Or risk one of them losing a piece of their's.
Nylon is much cheaper than leather and doesn't require the same maintenance in the long run.
Simple and Cheap are the two best words for an Explorer Uniform.
I suggest a different color uniform shirt than what the sworn members of your department wear.
If the sworn members wear all navy blue, then I'd get black pants with a light blue shirt. If the sworn members wear tan over olive drab, then I'd suggest gray over black. And so on, lighter color on top, not the same as sworn officers to avoid mix up.
Get them a long sleeve and a short sleeve uniform shirt. Make them buy a clip on tie to go with the long sleeve shirt.
Dark pants that go with the shirt.
Ballcap and a Uniform Hat. Because god forbid something terrible happen, you don't want to be at a funeral or some other memorial wearing a ballcap.
I like badges, but they run at about $100 a piece. So I'd get an embroidered one on the shirts.
Have a jacket pool they can take from too. Jackets can just be black for cheap costs and black jackets look alright on any uniform.
Here's the security section of Quartermaster, has some cheaper selections for clothing.
Just my dreams if I got to redesign my old post's uniforms. Good luck man, stay safe.