Hi John
Sorry for late reply.
Obviously if landings are bigger then price will reflect this.
I'd work on a round figure mate. When putting quote in you can add " this price reflects the size of landings and degree of soiling/staining" when I put price in I follow up around 10 days later, gently , like how was the price received by so and so block?? Then from answer you will get a feel for the job. As in was it too high, or any other objection. You can always knock some money off at this stage if you feel it may get you the job. Good luck. But I'd say your pricing is right. Things to look for are electricity supply. Some have none, some in cupboard, some have sockets with key and newer blocks have a funny socket that you need a adaptor plug to put in. Also is there a water source, outside tap.
Mark