The Thin Wall needs that cold, precise, slightly harsh early-80s sound — so you actually don’t need anything fancy. Here are some good options across different approaches:

Cheap standalone:

• Arturia MicroFreak — brilliant for angular, cutting sounds; very versatile for the price (~£200). Probably the top recommendation
• Teenage Engineering Pocket Operator — ultra minimal and cheap (~£50-70), surprisingly capable for simple melodic riffs
• Korg Volca Keys or Volca FM — the FM one especially nails that cold 80s digital edge (~£100-130)
• Behringer Model D or TD-3 — very affordable clones with that raw analogue character

DIY route:

• Moog Werkstatt — semi-DIY kit from Moog, simple patchable analogue synth, excellent learning tool
• Bastl Instruments kits — Czech company making simple, buildable synths, quite a cult following
• Music From Outer Space (MFOS) — classic DIY synth PCB kits, more involved but very rewarding
• Teenage Engineering Ortho Remote paired with a simple oscillator circuit

Worth knowing: The Thin Wall’s synth sound was largely a Roland Jupiter-8 and Oberheim — so anything with a decent sawtooth wave and a snappy filter envelope will get you surprisingly close.