since they air only has 1 thunderbolt and some usb2 ports, you're pretty pinched.
you could get a thunderbolt dock along the lines of the caldigit unit.. this has an hdmi and a pass-through thunderbolt on it.
you can then get an hdmi-dvi cable for oen monitor and a thunderbolt to dvi adapter for the other.
another option would just be a thunderbolt hub. neither solution is very cheap, but it willg et you wht you want. there are also devices for usb-vga conversion, but that's a last resort, imho.
i'm curious how well these will be powered (how much resolution and how laggy) they will be, but it should work.
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
Best Answer
The port between the Ethernet port and the Thunderbolt port is a FireWire 800 port.
On the MacBook Pro 2011 17" the Thunderbolt port supports up to two Thunderbolt displays.
As to using the FireWire port to support a display I do not know for sure other then this article essentially says no.