Can anyone suggest a good puppy playpen - either home made or bought (preferably inexpensive) already have the whelping bed which should be big enough for sleep and play until at least 3 weeks. Book of the Bitch recommends compost panels but these are quite expensive?

You can get a varity of puppy pens at good prices on eBay. From shorter ones, taller ones, ones with a door, 4-6-8-12 panels ones.

I purchased a LOT of these panels about 25 years ago, and I couldn't manage without them.  They are from a company (internet) whose name is VERY similar to England's biggest dog show.  (I hope I may say this.)
Here a little info from the internet:

Build your own size of puppy play pen   ...   Showman Puppy Pens and panels
are a very popular system, being a range of individual panels which are simply hooked together by plastic clips (supplied). This is basically a puppy pen made up to the size you need from a variety of single puppy panels, giving the ultimate in the variety of sizes and shapes of puppy exercise pens.
There is the option of a clamp on steel hook'n'eye which makes the pen even more secure and allows very speedy erection / dismantling

They are available in 3 heights, 22ins, 29ins, and 35 ins., and in several lengths. Panels may be plain or gated - there are two styles of gate available.
You just buy by the panel and make your own size.
You can even incorporate a roof!
The finish is hammertone silver/black.

A friend of mine used a human baby playpen for her last litter and it was great. Big breed dog and there was loads of room and as it was a toughened plastic type there were no bars for them to try and squeeze through, I just cannot remember the make. I'm sure it was bought on ebay or similar and not too expensive, worth having a look at.