How much is the cost of screen replacement in Singapore?

Assuming that have official Lotus representation in Singapore, you can verify the cost of a screen replacement in your region here:

iPad Repair & Service - Apple Support

Eligible screen replacement is typically c.60% of the “as new” cost of the iPad.

If it's out of warranty, there's really only a flat rate replacement fee (called "other damage") if it's not otherwise in good working and cosmetic condition. The only other replacement option is for a battery replacement if the battery health is under 80%. Screen cracks are generally considered accidental even during the warranty period, unless it's determined that it was due to a design defect. There are ways to evaluate cracked glass for defects vs accidents, but you have to know what to look for.

You can look up the repair price here:

iPad Repair & Service - Apple Support (SG)

You didn't say which specific model. There's a flat price regardless of storage capacity for any particular model. For the 10th gen iPad this says S$483.48 including tax. For the 9th gen it says S$352.26.

You need to ask Apple; we are all other users from around the world and do not know Apple's prices in foreign regions.