In reply to mikekeswick:
If you end up heading to Llanberis then the campsite in Nant Peris directly opposite the Vaynol Arms is cheap enough. I was only charged £4 per night earlier this year. There are other suggestions here:
http://www.ukclimbing.com/forums/t.php?t=316765&new=4677010#x4677010
If you really want to save money, there are some big rocks in the Pass that it used to be traditional to sleep under.
For Gogarth, I've had no problems sleeping in a van in the North Stack car park. If you actually want to bivvy out somewhere in a bag, then there is an alcove in the little crag overlooking the approach to Wen Zawn.
Have fun.
Andy.