Let me do a quick response.
Don't bu anything. Not yet. Consider all your options carefully, HDMI to VGA conversion and the other way can be a disaster.
....
After giving this some thought here's what I'm thinking. I am thinking you could buy yourself another graphics card that will provide you the output you need. Here's my reasoning. Doing the conversion of HDMI to VGA requires the use of an active adapter that only works in one direction.
Here's the problem. Some of the adapters people want to sell you are wrong way adapters you ask for HDMI to the VGA and they'll try to sell you the opposite. They might try to sell you a VGA to HDMI active adapter. And there's no such thing as any passive adapter that converts digital to analog or analog-to-digital. Not really.
The cost of a good active adapter may be about the same price as what you would pay for a good used dual VGA monitor.
Just about a week ago had to go through some of this stuff myself. At the present time you can pick up a very good television set with an HDMI input for a very reasonable price. You might consider the value of your current VGA monitor. What is it worth? If you want to keep using the VGA monitors I strongly recommend you go get a dual graphics card that has two VGA outputs. The card does not have to be expensive . In most cases any kind of PCI graphics card will outperform the built-in graphics on the motherboard. Actually, I really don't know what graphics your motherboard has, but the general consensus is that on board graphics are never as good as any kind of PCI graphics.
Now if you really, really want to do the HDMI to VGA conversion, you can get such things available at Amazon, New Egg and even eBay. Of course, you need to be careful when shopping on eBay. What you want is an adapter that goes from your video card over to the VGA input.
HDMI is the future for digital display systems.
I realize this is longer than what I had intended. In short, you have to have an active adapter to convert the digital signal to a VGA monitor. Check and see if the monitor has any other input options. Quite a few monitors nowadays have some kind of DVI connector. The DVI connector is most often a digital only connector, or in some cases it is a digital and analog connector in one package. My guess is that your motherboard probably has provisions for supplying either digital output or VGA output or even both. If both, it means that one monitor can be digital and the other monitor can be analog.
But I am thinking that for the price of just one active adapter you could buy a cheap dual VGA card. That's what I wanted to say.
Pardon me for the heirs you'll find in this. I wanted to respond to you right away and not take an hour or so to try to collect my spelling errors.