How fancy do you want to get? Rubber wheel are pretty cheap, but steel ones are pricy. Blade guides can be had for $30, or a really nice adjustable one is $400. Get a Cooks saw Mfg. brochure and look at some of the options and doo dads you can order. I have a pretty cheap mill, home made, but after using it for awhile I added better features, adjustments, guides. Its gets a little better every year.
Don't go cheap on bearings. Do not use open , roller skate type bearings on anything. With sawdust, lubes, and weather, they can go bad in a hurry and can be a pain to change. Make all your bearing holders open, and held in place with snap rings. Makes life a lot easier later. Put a lot of time and money in you carriage wheels, it again pays off later. Put a zerk fitting on anything that might ever need lubrication. Makes life so much better and things will last a lot longer.
Good luck, and as always take lots of pics for the voyeurs!