Ed, you should be able to pick up a used laptop[366 speed mininum, and Pentium prefered,128 ram min.] for around $350..

You should be able to pick up an older version of Acid Pro[3 or 4] for around $100[for recording multi tracks and rendering as MP3]..I would suggest you download Winamp 5.08[free] to playback media[MP3 and Wav], and VanBasco for SMF playback[free]...while you are at it ..get Powertracks[$29].
A midi/or USB interface will be needed..and I would suggest a soft synth[Roland VSC1]$60,for playback with in the laptop..

This set up will do all you require..
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