Only you know how much skill you have, but the project is pretty straight forward. I'm thinking make the carcass out of 3/4" oak plywood and face frame it with solid oak. Solid oak for the crown and the base. 1/4" oak plywood for the back.
50" is too wide for a bookshelf, so you'll need a center vertical partition to halve the distance (books are very heavy and the shelves would sag under their weight). The shleves are oak plywood as well, with a thick oak strip front and rear for stiffness. Support the shelves on shelf support pegs. Most of the time will be in the finishing, but you can save some time and trouble by finishing the parts before assembly (don't finish where you're going to glue, of course).
There are some excellent plans available from Woodsmith magazine (check www.woodsmith.com
). I built one for practice out of birch plywood and pine (before making a couple out of cherry) and it was surprisingly easy. Everybody wants the thing, but it's got my decoy collection on it now, and there they stay!
As for cost, you're looking at probably four or five sheets of 3/4" oak plywood. two sheets of 1/4" oak plywood, and I'm guessing about 40 to 50 bd ft of 4/4 oak for the face frames, crown and base. 1 to 2 quarts of finish, And your time. No idea how fast you work, but it sounds like it's a good 20 to 40 hour deal (it would be for me anyway).
One last bit of advice: 22" is too deep for a bookcase. More like about half that. Most books are between 5.5" and 8.5" wide. A real honker might go 12".
Go fo it!