Gigaset Additional Handsets?

I have a Gigaset S850A Go and Go Box 100 base station, it can handle 6 VOIP accounts - what are the cheapest additional Gigaset handsets I could buy that would work with the Go Box 100 base station?

Gigaset has a compatibility checker which may be some use?

I've got a couple of C430H handsets (Superseded by the 430HX) with my N300A and they work well.

Thanks.

I like my C430s which I use with N300s. You may find life easier if all the handsets are the same.

I recently got some C620H handsets to work with a GO box and S850A ... The cheapest way was to buy a triple set with a PSTN base station at just under £75. Singles were £40, twins £70 and the triple £75 although the same supplier now has them at £90. http://www.ligo.co.uk/siemens-gigaset-c620a-trio

They may not be the cheapest handsets but they do feel good and have good overall functionality Ligo also do trio sets of the C430 and C530 which are a little cheaper. As far as I know the very cheap bottom end handsets are not compatible with a GO box..