At first glance, the answer should be easy. Hop into any shopping mall today and you will find at least one cake shop. But the fact that you google search for it only means that you want something more or different that a typical cake shop could not fulfill.
Of course there are cake shops that focused on customised cakes. But they can be expensive. So more people tend to look to Internet and through friends' referrals for alternative bakers i.e. home bakers, online bakers. Their prices tend to be more competitive - though not always the case, and they often can go the extra mile for you; speaking from personal experience - flexibility is definitely a key feature of these alternative bakers.
There are a couple of other factors you will probably use for consideration too. They are quality, reputation and pricing. If your friends had tried the baker's service before, it's the best feedback you can get. Otherwise you can usually find reviews on the baker on Internet. But be aware of people who write good things about themselves, and others who write bad things about their competitors- worst, they are masquerading in forums and blogs with hidden identities that you do not know who is speaking the truth. Another good method is to go to the baker's website to view the pictures (pictures speak a thousand words ya), check out testinomials too. But then these could be engineered too. So read with caution. Another place to go to is the facebook. See what others say about the cakes made. I guess you will probably also choose based on gut feel. Contact the baker. Discuss your requirements. You will know there and then. ; )
As for pricing, home bakers usually are self employed and do not have workers. So the chief baker is himself or herself the only baker to bake and decorate your cake. Naturally the time cost will be higher. But think again - you are getting the most value for your buck; having your cake made by the chief baker. Isn't it great? Most other established bakeries will probably have tons of junior bakers fulfilling your order. On charging, bakers also assess the difficulty level and the size of the cake to determine the customised cake price. More difficult and bigger - more expensive. Simple equation.
And as for where to get your customised cake in Singapore? I had to be honestly bias. Visit my BakinCalf website especially the section on customised cakes.. Otherwise you may be interested to learn to bake your cake! So you can still "have your cake and eat it". ; )