MacBook – 13” Mid-2012 Pro, can I use FireWire to VGA for a triple screen setup

As far as I'm aware, you can't run Target Display Mode from Mini DisplayPort to Thunderbolt; only like to like or Thunderbolt to Mini-DP.

See http://support.apple.com/kb/PH14264

No, that 3-in-1 adapter will not drive multiple monitors.

What you need is either a system that combines 2 monitors, or a system that chains them. While DisplayPort allows for daisy-chaining displays, this only works on supported hardware. This means your monitors need to both have two DisplayPort connectors and official support from the vendor and inside in the chipset to make this work.

I believe that you aren't going to buy two expensive chain-able monitors since, well, you don't want to buy an expensive adapter ;-) The next stop would be stuff like Matrox's DualHead2Go. That is a device that allows 2 displays to be connected to a computer as one big display. http://www.matrox.com/graphics/en/products/gxm/dh2go/digital_se/ It does cost quite some money, so it might be in your category of 'expensive adapters'...

The problem with your question is that it is rather specific. It's a niche that most people don't even know about, and not a lot of sales or development is happening there. While it could probably be done cheaper, there simply aren't a lot of options here.

Just remember: one video port can only ever drive 1 display, unless it's a daisy chained display port system or a device that turns 2 screens into 1 big virtual screen for the video port. There is no cheap 2-in-1 adapter to make this happen.

Small addition: you might be able to solve your problem with a USB DisplayLink adapter if you do not need 3D video or accelerated 2D video. It's a video card with a USB connector on one end and a video port on the other. It won't be fast or high-performance, but if you simply want more desktop space, it might work for you. You would end up with one of these: http://www.displaylink.com/shop/adapters