dude as machine head said the hooking scene in Paris is very poor.
First of fall, I would not advise you to go around St Denis for cheonging, I think this place is kinda dangerous for a Singaporean, streetwalkers there are often east european gals employed by some Albanian or Ukrainian mafia and a french buddy of me had some problems with one of them. He brought her to an hotel and the girls pimp tried to steal money from him using a knife... If they do that to a french local, what they will do to a tourist!
there r many PRC hookers in the 19th 'arrondissement' at night in this place between 'colonel fabien' and 'belleville' prices are approximatively 40euros (80sgd) for poor services.
if u like latina shemales u can try the 'bois de boulogne' but this place is just so scary ahah I tried one time and got a good BJ for free as TS there are kinda horny and if they like the guy they can provide u free sex, but the normale rate is 20 or 30euros (40 to 60sgd).
To be honest with you, ull probably be upset if u cheong in Paris as this is far less funnier than in Singapore.
I will also advise you to find some local gals in clubs, it is not that hard, you should go for 'erasmus' parties on thursday nite (parties for international students so lotta choices of gals, swedish, german, french, italiano, etc..).
Try also clubs in Champs Elysée on week ends
There r also parties called 'afterwork' which begin around 7pm where business people meet after their working days and office girls are just so horny there, I dunno why. Its always cool to get ONS with some high profile french ladies
Btw be prepared to find lotta people who dont speak english, ull be impressed by the number of french who will not understand u
try to find a french buddy who can bring u in the right spots and avoid to be cheated, its not always easy to be a tourist in Paris