I done 3 jobs monday and earnt £100 i used a litre and half of chemical it costs £30 for 5 ltrs so i don't think i'l put myself out of business and as for training i went on the day course got my certificate and my df licence and iv'e got over 2yrs experience using df. 
You need to up your prices bro... That 5 litre should be earning you more!