If you are looking for a cheap “budget amp” for your AirPlay Setup, have a look at the Lepai LP-2020A+. It’s a really small mini amp which can be combined with “passive” speakers for a small and cheap AirPlay Setup (see also How to “enable” existing Speakers for AirPlay).
The Lepai LP-2020A+ is an cheap mini amp with 20 watts per channel, two inputs (RCA/Cinch and 1/8-inch stereo mini jack) and bass and treble controls. You don’t need to select the inputs because they are both hearable if there’s a signal.
The Lepai LP-2020A+ is designed for 4- or 8-ohm-rated speakers like most of the stereo systems. So you can connect it for instance with common bookshelf speakers.
Considering the price, the Lepai LP-2020A+ is a no-brainer: It’s available for about 15-25 Dollars/Euros in the US and Europe. You can get it on Amazon, Ebay, etc. The power supply is included (it’s external).
Size of the Lepai LP-2020A+
The Lepai LP-2020A+ is really small. You can see in the photos that it’s a little bigger than an Apple TV and really compact compared to standard Hi-Fi Components (Receiver, DVD Player, etc.). I really like the fact that this unobtrusive form factor helps placing it in the living room (needs only little space; doesn’t look “ugly”).
AirPlay Setup with Lepai LP-2020A+
As explained in the article How to “enable” existing Speakers for AirPlay (section “AirPlay for a Stereo system or Hi-Fi Amplifier”) you can use an AirPort Express for streaming music (connect it either with mini jack<>RCA or mini jack<>mini jack to the Lepai amp).
For videos, you could build for instance a system like shown in the following figure. Instead of the TV speakers, your little audio system plays the audio. To achieve that, connect the Audio output of your TV with the Lepai and mute your TV.
I think the Lepai is a nice way to extend your AirPlay Setup and lets you pick your own speakers. I like the small form factor and the ultra-cheap price. It’s more than loud enough for “standard use” in a common room and sounds good. Disadvantage could be, depending on your use, that there’s no remote control.