The cheapest adapters are the ones that come with some notebooks. I not sure how to answer this question these days with all the new types of connectors on monitors.

My brand new Power Mac G5 came with a VGA to DVI adapter. I am using it to run my 6-year-old Sony monitor on that computer. I was quite amused when I first opened the box for this monitor six years ago. It came with a CD on which was stored Windows drivers for the monitor. I chuckled a bit as I dropped the CD back in the box, extracted the monitor, plugged it into my then brand new G3, and just started using it. No fuss, no muss.

It's important to know the age of the Macintosh and the PC monitor in question. All current generation Apple Macintoshes (G4/G5) come with modern graphics cards (ATI and Nvidia) which support SVGA (HD-15) and DVI. Thus, all you need to hook-up a Macintosh to a PC monitor is the supplied cable that came with the monitor. No adaptor needed. Just plug-and-play. Currently, I have a Apple G5 and I have it connected to a Dell Flat Panel 19" LCD monitor. I can use either the HD-15 or DVI connector because the graphics card supports both -- note older G4s only supplied a HD-15 analog graphics card. But you'd still be able to use it with current PC monitors since most new monitors come with HD-15 connectivity. In my case, Dell supplied both cables when I purchased the monitor. This is usually the case if it supports both HD-15 and DVI. If the monitor didn't come with a DVI cable just pick one up at Best Buy or CompUSA. You'd have to do this even if you had a PC. Older generation Macintoshes (Prior to G3's) did use a proprietary video connections (Apple Display Connector -- ADC) and required an video adaptor if you wanted to hook it up to a non-Apple monitor. But those days are long gone. :) Today, Macintoshes support standardized hardware specs such as USB 1.1, USB 2.0, Firewire 400, Firewire 800, ATA, SATA, HD-15, DVI, PC100, DDR SDRAM memory, AGP, Bluetooth, wireless, 10/100/1000BASE-T. All parts available at your local CompUSA or Best Buy. Note that HD-15 and DVI are commonly referred to as analog and digital respectively. Here's a few connector images... http://www.ramelectronics.net/assets/images/HD15-MVC-series.jpg (HD-15/Analog) http://www.bluejeanscable.com/store/dvi/dvidplug.jpg (DVI-D/Digital)

If you buy a mac mini you can because there are videos of it on youtube