SO,according to your statement you will be paying tax on 30K which with class 4 nic will be £10K,best part of £200 a week ,you obviously have other income that takes care of your personal allowance,
Anyway,well priced compact work shouldn`t really be sold for any less than 6 times gross monthly take so its worth every penny of 15K. If con roofs,gutters and prostitution havn`t been included in turnover i may be interested so long as there is scope to lose a few/dump/gain a few and the locals are not too interbred.