I have been surprised by the variety of prices for "french press" coffee makers. This is a fairly simple apparatus that keeps you from having to buy coffee filters, but may leave some of the smallest bits of coffee grounds in your cup. To use it, you mix ground coffee and hot water and then press down a plunger that keeps the grounds in the bottom of the container while you pour the coffee into your cup. It does not require electricity, so, like the model described by Lucas, you can use it when the power is out as long as you have another source of heat.
As with everything else in the known universe, there is a Wiki article about it:
http://en.wikipedia.org/wiki/French_press.
Here are the results of my price research in Xela:
& Cafe - Located next door to McDonalds on the Parque Central. Only has plastic models. Price is Q200 to Q360, depending on size.
Cemaco - Near the Pradera mall. A glass and stainless steel model for Q100. It looks just like the one pictured in the Wiki article. Works just as well as the plastic model, looks nicer in your kitchen or a commercial cafe (where I use it), but may not be as good for travel as the glass is very thin and fragile.
Almacen El Aguila - On 6a. Calle between 10 and 11 Avenida (half a block downhill from Parque Central). Has a model almost identical to the one at Cemaco for Q40!. Now I know where to go for a replacement if we break the one we bought at Cemaco.