Present owners of Neo, Model Car World, have a huge selection of models on eBay, often at reduced prices - there's both the main branch in Germany and a smaller one in the UK (with reduced selection)
The other special customer of Neo, Modelissimo is also a german dealer, and they too have a vast number of models for sale on eBay. I find that they tend to be slightly cheaper than Model Car World on most occasions.
For the very best deals on Neo, though, it's a third german dealer that takes the prize. It goes by the name of Merge Left and they always have a (albeit limited) selection of Neo at very low fixed prices (down to just under £20) as well as some auctions where you can really hit the jackpot, especially if you're looking for semi-modern japanese cars like Nissan Laurel, Mazda 323F, Mazda 626, Mazda 929, Mitsubishi Sapporo and Galant, Toyota etc. - these can sometimes be won for less than £15... and that's for a premium quality resin model. That sum will normally not even get you a standard partworks model!
They also have several of the US cars from the mid 70s and 80s, but for these you can expect to pay somewhere in the region £25-35, which is stil a LOT less than normal retail price.
I've bought a bunch of nice street cars from them, mostly japanese, but also some obscure german ones like Lloyd, Borgward and Hansa.