My contractor charged me only S$100 excluding the chemical, if plus the chemical he charges S$150
End of the day i went with a contractor from JB, charged me S$120 for the washing and chemical, did a good job, you can find the contractors usually around Jalan Harimau area in JB, they have a row of shops there
You can find these guys doing these cleaning services on locanto/criagslist classifieds as well, they charge usually S$10/S$15/hr, its pretty common