He SlimeShady, whoever told you that £400 for a portable gunge tank was too expensive should try and build one themselves!
When i built my first it was very basic and a poor design, but i spend nearly £100 on wood alone before any screws/nails/paint - and not to mention the plexi-glass at £30 a sheet for 2mm thickness - and my tank needed 2 of those, but because i used the thin stuff it broke easily when one of my models slipped and cracked it. So now i use the 4mm sheets and it holds up much better.
However my gunge tank was nowhere near portable. It could be flat-packed but that's all.
The gunge tank i'm currently building is going to be almost double the cost of the first one, but "Katie's Gunge Tank Mk2" is far better and has been through a 3D design process and i've even invested time and money into studying fluid dynamics and liquid particle physics - so i've gone a bit OTT but it should all be worth it
Good luck to anyone else who is attempting to build one of these! It's not as easy as you might think...