For the DIY freak, replace the IRFP250 with the newer IRFP260 which can handle 49Amps and you have an extra safetymargin
Well, even at TopLoser bargin prices 850 GBP is way too much for a PhD student, especially for pretty much a bunch of MOSFETs and heatsinks
(even small 300W DC loads are around >300 GBP, you can buy a scope, a lot more complex instrument, with that kind of cash).
That's why I want to build my own and I have a lot of parts already (ADS1256 ADC, 16 bit DAC, big heatsinks, OP27s, AD8628s, everything either second hand or Aliexpress/eBay). Thanks for the tip with IRFP260, I've checked and they can be had cheaply at Aliexpress so I might consider using them instead.