Wood pellets have the same questionable issues as shavings (although many people use high quality shavings without issue). They also break down to dust when wet (and to some degree when dry). The Thirstybed isn't much good because it's designed to be used dampened (breaking up the pellets) which is fine for horses but not so good for guineas.
Megazorb is another wood based option (wood pulp) it's sterilised at high temperatures and dust extracted and is relatively soft and very absorbent. A lot of people think it's great but I have heard some people say it's dusty though.
There are various chopped straw type beddings (wheat, rape, hemp, flax). I don't recommend chopped wheat straw and it has poor absorbency but the others are meant to be better (had recommendations for aubiose (hemp)).
There are various chopped card beddings (finacard, green mile, ecobed, ecobale) but they are in a similar prince range to fitch (some cheaper), although I feel they are slightly longer lasting between cleanouts.
There is always the potential for mixing two beddings to gain different advantages (e.g. softness and absorbency) and reduce costs.
Also, make sure no natural oils have been added as these are irritating to the respiratory system if you have to live with your face in them.
This site has a good selection.
http://www.gjwtitmuss.co.uk
