For some of us winter gives us the blahs. I'm one of them. After getting off work I just want to crash on the couch and wake up about mid-spring. It's a constant push though to keep from the couch. Hobbies, such as mountain biking help. Sure, January here in Western NC is the month of mud, so that rules out trail riding. However, it makes it prime time for bike maintenance. Suspension, brakes, bearings, pivot points, cables, all need some tlc and now would be a great time. Many of our states are snow covered. Maybe you can get out on a fat bike, maybe you're too snowed in. Plan on that maintenance and get it done. You'll thank yourself when spring riding season gets here, especially since many local shops get backed up several weeks with repairs and tune ups!
We need to keep in shape as well. I've found you can get in a great workout with resistance bands, and the sets can be had for relatively cheap. Couple this with any number of inexpensive additions and you have yourself a great little "disappearing - reappearing home gym". I'm talking ab wheels, push up bars, swiss balls, even a set of adjustable dumbbells can be stashed under a couch or in a closet. Nothing I think can replace saddle time though, and this is where a trainer comes in. You can find them used for around $50 on up. You can even find them new for about $50 on up. The choice is yours. Noise a concern? Rim drive ain't cheap. However, you could pick up an inexpensive wheel and swap that on and off with a slick or semi-slick tire to keep hum to a minimum. All in all, you'd be spending less on a trainer and wheel/tire setup than a decent stationary bike, and getting to log miles on YOUR bike, keeping you used to YOUR bike.
Entertainment should focus at least in part on mountain biking to keep you motivated. Just like people listen to recordings for positive thinking and other means, watching YouTube videos and other purchased vid's can help keep you pumped for riding, even when warming the couch. Heck, Redbull TV is chock full of great content, and it's free. Your local bike shop got a pub-bar-hangout scene? Head on over! That's what it's there for! Keeps you in the groove and you become more of a regular. Besides, when you need something done in a pinch they'll be more likely to recognize you and hook you up.
All in all, I hope you continue to keep your head up and I was able to offer some good ideas. I'm keeping this one short today, so go do something!