first of weigh the sink in......... then see if you can hire a digger and driver.......average price is 150 a day and a good one will piss that in a day!!! ask him about getting rid of the soil, he will no someone for that...........then find a firm that crushes concrete round your way as stone is around a tenner a ton off them, compared to £50 a ton bag for mot1 from a builders merchants..... get the stone for inches below the level of the slabs, whack it and then look around for slabs, you will find someone wanting rid if you look hard enough lol and then get some sand, cement, mix it in