There's the Zoom FP-02 as well for about £50-ish.
Have you looked at the POD Go instead of the Helix Stomp? There's the same amp/cab/effects models, just a slight reduction in functions (single amp/effects chain IIRC), but it does have a built in expression pedal. These aren't much more than the HX Stomp.
A fair bit more is the Helix LT, but it does have the full Helix functionality, as well as increased connectivity options and the expression pedal.
To achieve a similar outcome, but with less outlay, have a look at the old HD500x, though you do need to buy the HD Bass pack. You can pick one up a good second hand one for about £200-250. Add about £20 for the Bass pack, or about £75 for the Fully Loaded pack, it will give you loads of options, as well as having loads of connectivity options for studio/live uses. Been running one for a good few years now, still very happy with it.