Just chipping in to give some additional info. Moving from KL to SG, you have to give up certain ... comforts. Ringgit-to-Dollar, rm2.5k/mth you can have a nice comfy gated condo with swimming pool, and drive everywhere in a local car. sgd2.5k/mth you can only get a <1000sqft hdb (i.e. public housing) flat with no facilities, and have to take public transport everywhere.

In addition, the first-month relocation & settling-in money you need to cough up can be quite an eye-opener - when moving in to my current place (rented) I had to cough up over $12k for agent fee, first month rental, 2 months security deposit and furnishing. If your company doesn't cover your relocation then you have to further factor in the costs of packing and shipping all the contents of your KL place to SG as well.

Other than housing & owning a car though, everything else is less than a sgd1:myr1 ratio. quick & dirty example, marutama ramen in MY is like rm20 a bowl; in SG it's $14. Also, just commenting on river's $5k estimation, that's about the average basic monthly expenses for myself + my fiancee without kids - and not including all those "miscellaneous" stuff that every month also sure got - things like birthdays, needing to fly back to M'sia for whatever purpose, holidays, shopping, savings, etc etc.

if you *fully* move to SG i.e. you are employed by the SG entity and paid in SGD, no need to pay any tax to Malaysia.