200 x 300 ft = 5,500 square metres... That
is big.
You'll want a self-propelled rather than push mower and that will bump up the price.
Few domestic units will be rated to run for long enough continuously and you may/will need to factor in rest/cooling down periods for the motor. You
will need two sets of batteries; another extra cost.
An electric start petrol mower may not have such limitations? Self propelled or even small ride on. Again, though, those will likely exceed your budget - even second user from lawnmower places.
Einhell do one that's £525 ish from some outlets (
Wickes) with 4 x 18V 4Ah batteries ... and can take all 4 for extended runtime. Still only recommended for up to 700 sq m lawns though!
GP-CM 36/47 S HW Li (4x4,0Ah)
www.einhell.co.uk
