I've won an Isolette with an Apotar lens, which is, apparently, middle-of-the-range. Probably an Isolette II. The seller wasn't knowledgeable about cameras, so it couldn't get all the craic, but it was less than £12 with the postage, so, I can live with an element of risk as to the condition, (which could consist of leaky bellows or solidified lens lubrication, apparently). We shall see.
Filters will be the next thing: 30mm push ons, aka A30. Not plentiful.