I'm not sure buying pieces is your best bet for this. Specialized Hardrock or better frames from about 2000 onward have disk mounts, and from about 2005 mostly have disks, and so probably do other manufacturers' bikes. You can find a bike like that for probably 2-300 bucks or less, then $50 for that fork, while I bet a frame+fork+groupset+wheelset+tires+cockpit is going to run you well up over 500 and make you do a lot of assembly work. Will it be done by winter?
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."