If you cant answer that question you probably dont have the work or are at that point,
Its different for everyone , but surely the answer is enough to pay expenses , wages, tax vat? and make a profit , how much profit depends on you at the circumstances of the area and business.
Its a headache having staff and running it all so it wants to be worthwhile for the hours you put in
I reckon the £300 quoted is the bare minimum for two guys and a vehicle .
Probably gonna want to get another £50 - £100 a day to start seeing a reasonable profit
But it all depends if you are paying two lads "self employed " £50 a day
Or employing properly paying , and paying VAT etc