http://www.thekitchn.com/how-to-roast-beets-in-the-oven-cook...
Again, 3 minutes of prep time for 2 or 3 roast beets. Both red and yellow beets are amazing. Just don't freak out the next morning when you pee.
And now that I think of it, these recipes work great for asparagus. It's a little trickier though: if overcooked, it gets mushy.
The one expensive thing you should buy is a good heavy knife. Buy good olive oil too; California Olive Ranch olive oil is widely available in CA and reasonably priced
http://lifehacker.com/the-most-and-least-fake-extra-virgin-o...
http://www.nytimes.com/2011/10/19/dining/californias-olive-o...
While I'm raving about roast vegetables in general, roast fennel is one of the best things you've probably never eaten. Really, give it a try.
http://www.simplyrecipes.com/recipes/roasted_fennel/
Roasting veggies in general: http://www.marthastewart.com/270268/how-to-with-allie-roasti...
eg this tastes amazing, and you're looking at like 2 - 3 minutes of prep time, and makes enough for a couple days. Ditch the thyme if it's a hassle, and you don't have to cut the cauliflower that finely. http://www.foodnetwork.com/recipes/food-network-kitchens/roa...
Baked chicken (buy it skin-on -- it's both cheaper and it retains moisture) is similarly easy to cook. Dump random spices on it, roast. Here's a recipe http://www.gimmesomeoven.com/baked-chicken-breast/
Most people I find who don't like chicken breast dislike it because someone -- probably parents -- cooked the shit out of it and it was dry as a bone. That's not how chicken breast should taste. If your chicken breast is dry you're overcooking it. Pay the $1 or $2 premium for locally raised, never frozen chicken breasts at your local butcher. You'll taste the difference. Feel free to ask them how to cook it; generally they'll be happy to give you advice.
Sweet potatoes taste great with nothing else and require you to score them and put them in your oven.
Roasted brussel sprouts are similar: prep time 2-3 minutes. Taste great. http://www.foodnetwork.com/recipes/ina-garten/roasted-brusse...
For that matter, get a crock pot. There's dozens of variations of a recipe like this: buy tough meat cut (and hence cheap!), roughly chop some vegetables, put in water in crock pot, let crock pot cook it for 8 hours. Come home to amazing hot food. I'm not exaggerating when I say 10 minutes of prep time, and it's enough food for 2 people to eat 2 large meals each.