Not at all intrusive. I happened to find mine on ebay for $400. Ideally, you want to find a seller that you can pick the machine up from yourself because shipping an arcade machine is incredibly expensive. The seller was located in the mid west US and I live on the east coast so shipping was another $200 - $250.
Anyway, when it comes to buying anything arcade related I recommend checking out these forums for a start:
http://www.arcadeotaku.com/ (GREAT place to learn about arcade stuff)
http://shmups.system11.org/index.php
http://neo-geo.com/
http://forum.arcadecontrols.com/ (never used it much, but seems pretty active)
Each one has a trading/buying/selling section. There are a lot of knowledgeable people who are experienced with arcade hardware and where to buy and sell things. Every once and a while someone will be putting up a machine for sale. I think it's even appropriate to post a WTB (want-to-buy) request so someone can keep you in mind for when they finally decide to sell their machine.
If you're impatient like I was, you can just check ebay and bite the bullet on whatever the shipping is-- or maybe you'll luck out and find one nearby. Try checking craigslist too. It'd be best if you can test the machine out yourself before you buy it. Make sure to research models on the arcadeotaku wiki and read their beginner's guide.