As a fellow noob, just getting into this hobby in the past few months as well, I'll outline some thoughts that might help. I've spent more time/money on my own build, but several friends have asked me to help them with "cheaper" builds. Here are some general costs for a cheaper build I've worked on for a friend. Keep in mind that this can be less attractive, but functional. The upside is that you can come back with more money later and spruce things up if you want. As others have said, if you really want a nice looking setup, your budget will jump higher than $200 quickly. But if you just want to setup a working cab, have some fun with it, and then decide how much further to go with your investment, here are my thoughts.
PM me if you want specific links/details, as I don't want to flood the thread with a bunch of eBay links and such:
Cabinet - Free (+gas). I posted on CL saying I was looking for a gutted/broken/beat up cabinet. I actually received several responses within a couple of weeks for everything from Free to $100. You can also just keep an eye out and search for "arcade" several times daily. They go fast, so you should check often.
Encoder - The super-cheap option is the $11 board from China/Hong Kong you can get on eBay. It's a Zero Delay encoder knock off, but works great. It's more limited than the I and J pac setups, but it's got plenty for a simple build (1 joystick, 12 buttons). I ordered two for a total of $22. Comes with wires for button/joystick connections and USB cable.
Joystick/Buttons - Again, going cheaper, you can grab 2 'competition' joysticks and 14 buttons for around $35 shipped on eBay (and you can pick your colors). That's enough for 2 players, 6 buttons each, plus a P1 and P2 button. If you need a few extra for admin stuff, you can pickup buttons for $1.50-$2.00 each in other auctions.
Lighting - LED strip lights, 5 meters worth, can be snagged for $5 or so on eBay. They run on 12V so you can literally wire them into your PC power supply with minimal effort. Great for cheap marquee or other lighting.
Control Panel Overlay/Marquee - Design your own, or find another someone has shared, print it at Staples for $12-18 on outdoor vinyl. You can do a marquee on regular vinyl for $5 at Staples too. Grab a sheet of Lexan or Plexi (I prefer Lexan) and slap it over your CPO, use it for the marquee if you don't have anything up there.
Add that up and you're still under $100. That's assuming you have the monitor/computer like you said in your OP. Again, this is a cheap build. Ideally you'd spend more money on each of these items to improve quality, appearance, etc. My friend loves his setup immensely, and the whole build was around $175, but it's not a showpiece or something gorgeous, it's a functional, fun feature he and his buddies use in his mancave while watching games and grabbing some beers.
Honestly, the biggest cost savings on a cheap build is the cabinet. If you can get a free one or cheap, you're golden. Be patient on the cabinet, see what you can find over a few weeks. Order or work on some of the other stuff in the mean time while you hunt.