Prices on eBay can be really high sometimes. You'll probably have more luck finding a decent deal on a local marketplace or something, even some game stores that sell used consoles. I've bought my first Wii U for $145 which was in a pretty decent shape.
There's no reason not to mod it. Definitely go for it,
here's the only guide. You can set up both Tiramisu and Aroma environments and switch between two when needed.
If you're talking about virtual Wii (i.e. vWii), you can safely mod it as well.
Here's the guide.
As
@luvcy mentioned, there's
NUSSpli and
WiiUDownloader for Wii U games (and some virtual console titles). As for Wii, I'm not sure as I download Wii games from a certain site we aren't allowed to link to. If you plan on using NUSSpli, you might as well get yourself a Wii LAN adapter as downloading via wireless connection isn't the greatest by today's standards (even with the LAN cable, it's only 2x faster).
I'm not sure whether Pretendo will ever be supported on vWii since it's a Wii without plenty of its original features.
Now, is Wii U still worth it? If modded, it definitely is.
With modded Wii U, you gain access to almost full Nintendo library through emulators and Retroarch (except for 3DS and Switch), plus many other retro consoles. Emulation quality varies but it's getting there. While many of its first party games got released on Switch with some improvements here and there, there are still a handful of games that probably never will (e.g. Affordable Space Adventures, Game & Wario, Kirby and the Rainbow Paintbrush, Mario Party 10, Nintendo Land, Paper Mario Color Splash, Wii Party U, Yoshi's Woolly World).