why not cop a used MPC and grab a cheap midi keyboard like a casio or yamaha, sub 100$ thing. That would work for what you want. The mpc has a dead nuts simple sampler to work with. Or still possible would be to grab a cheap pc Aprox 3-400, usb interface with 1/4" inputs, or phono imputs would be a plus if you already have a TT, and a cheap midi keyboard, keyrigs are really cheap, now were taking around 600$ use the last 100 on any number of things.
Now heres where dogma and fanboyism can get out of control, there are some seriously good tools on linux for working with audio, and its all free. Rock a real time kernel and your are experiencing far less latency, and while some hardware support can be dicey you can find a driver for most everything. I could list a bunch, or you can pm me if you want a mini build-out. And dont get me wrong, I love my mac, I am about to fall head over heals for logic, I know I am, but theres still that dirty chick on the side that does exactly what I want her to do, and shes always eager to learn what she doesnt know. Thats like the most base way to put how the linux systems I have are. If your familliar great, if not spend some time looking into it, its a great way to do what you wanna do for a lot less money. and when you make good money off your work, invenst in whatever toys you want to!