Welcome to the fun!
$600 is a good figure to play with, that way you may have money left over. I'm not familiar with Pirate's motors, but it is most likely the standard variety Chinese one you can get from anyone. The most important thing when buying a motor from anyone is their customer service and/or any type of warranty, but as far as Pirate Cycle goes, you should be good there.
$150 bike is easy to find on Ebay too. I got a cruiser for $136 delivered from a place that deals strictly with Greenlines and it's been a good bike. Another alternative is to buy just the frame and put it together yourself choosing which wheels you want instead of the cheapo's that usually come on cheaper bikes.
Hope this helps.