JUst having a quick glance and i'm no expert, i'm just finding out myself as i go along.
Electric start engine ebay, £225............item number 260965229447
Interpump ebay, 200 bar, 21 LPM, £568............item number 171633946834
You'd then need a 12 vollt battery for it, some inlet adapters, and outlet adapter /unloader valve. So thats maybe another £100.
It takes seconds to bolt a pump onto an engine as they are just like meccanno sets
Thats roughly £880 ? For a brand new turn on the key .
As you say you can just fit it on a skid plate to leave in the back of the van which is basically what i have done.