Jebus, £37 is eye watering enough for a 6mm model!
Mind, 1/300th scale battleship kits are bloody expensive so I shouldn't be surprised...
Can you kit bash some old tupperware or a 20mm scale tank a la Ian?! Or given in 1/300th it's what, 11.6 cm's would a 28mm-ish tank chassis be better?
Assuming my maths is right