Hi Simon,

There are a few things worj mentioning here - there are two types of Venetian plastering - textured and polished.

Textured is cheaper than polished, as you apply the plaster with a roller, then dip you pain(s) in a sponge and either dab or rub in. They now do gloves similar to oven gloves that is quicker, and are only around €5 each.
Polished requires the same base plaster rolled on, then you tint the colour(s) in a different plaster base that then gets applied by spatular colour at a time in patches until the wall is covered. The result is that the colours interweave. Finally, you burnish the plaster when it has started to go off, and this gives the polished shine you see. You can also cover them with wax.
As for costs, it depends on the whcih one you want. Drop me a mail, or if you have email that can take a few meg drop me your mail address and I can send the photos of the price lists in the store that I took photos of!

Regards