Eldgreen, yagis are fairly easy to design and build, thankfully. The directors (more the better) are half wavelength of the channel you want. In general, the feed dipole is 5% longer than the directors, and the back element is 5% longer than the active element. A corner reflector is just an angled, larger helper to the usual reflector element, reflecting more of the wave back to be "recycled" towards the front, instead of just passing by, unused. Think of it akin to a helpful "catcher's mitt", or a shoreline breaker, folding the waves back.
Hope that helps. Feel free to ask more questions as needed. (And have a Merry Christmas, one and all!)
Btw, if the only material you can get is wire, considering your budget, the elements can be better made by using either folded dipoles, which mimic thicker elements, or bowties, which act similarly, mimicking conical elements. Again, these catch more of the wave. And remember, don't be afraid to experiment with the base design of any antenna. You won't know until you try it, and something may work better for a situation.
PS. Almost forgot. A corner reflector is fairly simple as well. It is, in essence, just two flat reflector grids, angled forward to reflect waves to be used, like so:
Yagi <---- (((((( RF waves
(As seen from side, left being the corner reflector, to the back. Think of those waves hitting the back, and being reflected forward again.)
Others here know more about the specifics of the GH than I.