The nice thing about buying Weston's is that they are readily available in a variety of conditions and there are real bargains to be had. You can get meters from the 650 to the Master 3 for ten pounds or less. You can keep your eyes open at boot fairs (garage sales) and if you go to enough you'll come across them. Prices and conditions will vary and be prepared to haggle on price. I bought a brand new Euromaster in the box for £4 at a boot fair!
A more fruitfull source is ebay - you'll find lots of them there. Problem is you can't test them so make sure you establish with the seller that the meter works i.e. the needle moves across the scale when exposed to light. Westons are very reliable but the photoelectric cell can fail and if it does it's very costly to repair - in fact, don't even think about it! Don't be tempted to bid beyond what you want to pay. Prices vary crazily so track each meter and bid at the last moment if you want it. If it goes for a price above your range, don't worry - there will be more coming along! For UK collectors, US sales (available to UK) are generally a lot cheaper even adding postage.
Now here is what you should be looking for:
Westons made in US and UK are different - the Weston 3 UK for example is black, whereas the Newark version is stainless steel.
Oh, and if you want one to use, a Weston 3 onwards makes a good workhorse.