Honestly the most cost effective way to do this would be to get a midi keyboard and turn it away from your computer. MIDI keyboards would be a lot cheaper and you would get more experience learning to use the samples/synths you have.
I had one of these last me around 12 years. If you can find a used one it would be well worth it though it does use the old fashioned 6 pronged midi in/out cables and no USB compatibility.
http://www.roland.com/products/a-37/
I now use one of these cheapos.
http://www.m-audio.com/products/view/keystation-49es1
Which i'm not overly fond of because of how the keys feel. Unweighted keys never feel....real...
Another option is to get a simple Casio that you can use for practicing away from your computer for $100 and save the rest for your studio.
Just to go off on a tangent, the best way to learn music is to play music. Sitting in front of a keyboard practicing sheet music for hours on end is how I and many others learned back in the day and frankly it's a really outdated way to learn music. I emphasize MIDI keyboards because some of the best musical experience you can get is from loading up the music you already like on your HDD and playing along with it, figuring out the chords and melodies by ear. Do it enough and you'll recognize patterns you can use in your music which is the real key to actually learning anything. Learning to read sheet music does help some when you learn to read music vertically but it's not 100% necessary. It's important to remember that when music went digital people who learned music "the old ways" all had their legs kicked out from under them. Finding your own way of learning whats out there with the combination of resources available is all part of the fun of learning music today.