eBay has a 20% of power tools promotion. You have to add both items to cart to get the free shipping (otherwise it's $9 per item). Once in checkout apply the coupon SAVE4FALL to the order.
It's sold by Factory Authorized Outlet (Authorized Milwaukee dealer). I've purchased two items before and have not had any issues.
Final prices and link for items:
M12 10oz Caulk gun - $103.20
M18 Inverter power supply- $79.20