To effectively use a Equalizer, you have to first test your room and then equalize out any inconsistencies you find. The equipment to do this (test) would cost about £150 (best guess) and assumes you already have a computer.
However, that is not how most people use an Equalizer. For most this is simply an extension of the Bass, Treble, and Volume Controls. Bump the Bass, Boost the Treble, and Emphasize the Midrange which effectively is the same as turning the volume up.
It is not about Equalizing at all, it is about boosting the sound in your preferred ranges. Though it is your system, you can do what you want if you are happy with the results. But those results are based on a Glorified Tone Control not on Equalization.
As Paul points out, modern Room-EQ or Correction can actually do what an equalizer was intended to do. The Room-EQ tests the room at a range of frequency bands, and corrects those frequencies based on the readings it gets. Though it does this, most often, in the digital domain.
This is easier if Room-Eq is built into the Amp. Most, by a vast majority, of AV Receiver have Room-EQ/Room-Correction. A few Stereo Receivers have this.
To make Room-EQ work as a third party device (DSP), you pretty much have to have a Pre-Amp/Power-Amp system. The EQ Device would be placed between the Pre-Amp and Powe-Amp. These types of device tend to be a bit more expensive. Though I don't have specifics on the price or the devices. I think the miniDSP-HD is about US$205, not sure of the UK prices.
For a vast majority of people, I do not recommend an Equalizer. There are other complications in connecting the device as well. Even an Equalizer works best with a Pre-Amp/Power-Amp. So - NO - not recommended for most people.