i reckon you want at least 6k from 2 guys
4k from one, i wouldnt consider doing it for any less, not that it cant be done, but the returns wouldnt be worth it, wages, fuel, insurances, tax, vat etc
2500 a month from one guy is definitely low, the guy is working very slow or is on underpriced work.
If you are happy then fine but i think you realise you need more return as you posted so you need to find out whether a, your work is underpriced or b, your guy is too slow!!