Priming models (on the cheap)

Priming models using a brush takes a lot of effort, so you're usually better off using a spray paint. However, spray primers tend to be expensive. GW's spray paints are around £10 each. Luckily, you can use other spray paints, too.

Unfortunately, not just any spray paint will do. Being a naive miniature painter, I hopped down to a local hobby shop and asked for "any spray paint that sticks well to plastic and metal". They gave me a 'graffiti spray' (about £3). Sure enough, it worked by the specified parameters. It stuck well and covered the whole surface. However, it was prone to sometimes uncontrollably just spitting out large gobs of paint. By the time I realized this, I have primed a large number of models. Unfortunately, on smaller models such as infantry, the spray has visibly covered up some details. I'll let you be the judge of it:

Looking carefully on the model on the left, on the rightmost tentacle, you can see spraying marks - like small craters.

Same on these Daemonettes.

The Goblin King (intended to be used as a Great Unclean One) was completely ruined. I stripped off the paint later on.

I followed up with some googling and reading up forums. The internet's combined wisdom led me to buy a spray paint used for cars (about £2.5):

This gave much better results. I've primed everything ever since using this spray. It always covered well the "visible" part of the miniature. I sometimes needed multiple spraying sessions to cover the parts that were "hidden" the first time - inner thighs, buttocks, under wings etc. Take a look:

 I use this large cardboard box for mass priming.

All the fine details on Bela'kor are kept.

To sum it up, you really don't have to throw money out the window purchasing "official" spray paints. Just be careful and experiment with your paint before priming all your collection with it!