Only you know the value id of thought, the typical average for work that is say £20 - 25 ph is 5 x monthly, and 10 x fortnightly, but id of thought, if it was good work, long est, good payers, compact?, in an area that will expand, average price ie not £5 each but £30 each all has a huge bearing, like you say some is commercial, id want 10 x monthly easily!! but that is 27000 so will someone pay that only you know
What would you pay for it - honestly? There is your price!
Ps dont take advice on rounds off platinum NW lol