Honestly those quotes don't look that crazy for resale HDB in the current market, painful as that is to hear. Resale adds cost because there's usually more hacking involved, older pipes and wiring that need updating, and more unknowns once they start opening things up.
That said $65-80k for your scope does feel on the higher end. The carpentry at $18k is where I'd push back the most. For master wardrobe, kitchen cabinets and entryway storage that's quite a lot unless they're proposing full floor to ceiling everything with premium laminates.
A few things worth checking — are they quoting full hacking of existing tiles or just overlay? Because overlay flooring saves a significant chunk and for a resale that's liveable it's worth considering. Also ask them to break down the electrical in detail because $7-8k is steep unless there's a full rewiring situation going on.
My honest suggestion is get 2-3 more quotes from smaller renovation contractors rather than ID firms. ID firms have overhead and design fees baked into everything even when you don't really need the design service. A straight contractor for your scope could come in $15-20k lower easily.
Also your requirements sound pretty standard — no feature walls, no fancy built-ins, nothing structural. So you have room to negotiate or shop around without compromising much.
What's your actual budget target? That'll help people here give more useful suggestions on where to trim.