I'd plan on a weekend just to be safe, but it can be done in several hours.
The alt swap should take about 10 minutes unless your bolts are frozen, then add some time for beating, cursing & hitting with a hammer.
Cost really depends on the alternator you use, size & type of wire, connectors, fuse holders, etc.
My ranger 200a alt was about $250, about $100 for wire 1/0ga, probably another $30 for connectors. I already had some ANL wafer fuse holders & fuses so that saved about $40.
100% pure copper will have the most power transfer/less voltage drop but if you use CCA wire just make sure to get a good brand like knukonceptz because most of the other cheap brands will use minimal wire & super thick insulation to fool most people.
I got some cheap CCA 1/0ga wire that's smaller than my good 4ga wire.
My knukoncepts cca 1/0 wire is supposed to be equal in size to 2/0 but still just fits in 1/0 connectors.
My knuconcepts cca 4ga wire is larger than that cheap 1/0ga cca wire.
If you're gonna crimp terminals (cca wire does NOT like to be soldered) you'll want to invest in a good crimp tool like one of these:
http://www.amazon.com/gp/product/B003X51S00/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
They're a must have for larger terminals.
If you use 100% pure copper you can crimp & solder the terminals but most people don't have the proper tools to do the job so I don't recommend it for "noobs"
You'll need a fuse between the alternator & battery to protect against spikes too. Some people don't use them, but I'd rather be safe than have a burned up truck.