As of right now, a full set is $550. If you are capable of making the metal frame, cost will be under $500. Someone has already built the whole machine under $350.
Yes, that will be all you need to run the printer.
A lot of the cost will be shipping. If you can buy most of the parts from the same place, you should be under $300.
Kits are now available on kickstarter
Yes, that will be an option. Updates will be posted on the heated bed.
Yes, that will be a lot easier, but it would not look as nice.