15 m of copper pipe PER ROLL (50 ft) x 2 roll (gas+liquid) about RM 450. Need 3 x for your distance, so copper alone RM 1,350. Insulation is per 6 foot length at RM 3 per length, so RM 75, 4 wire 2.5 mm² (because inverter, and far away) per roll about RM 400 (90 m per roll, so can use for 2 a/conds, so RM 200 per unit). So far RM 1,625 in basic material costs only PER AIR COND. So 2 a/cond installation with distance of 140 ft is RM 3,250 in basic material cost.

Your quoted installation cost is cheap. Please check if there are any hidden costs, or if substandard material is going to be used, or if the installer has made a mistake. After started already and then they will come and say have to increase the price.

But forget all the above first..... I believe that 140 ft is over the maximum design limit of copper pipe length for most domestic air conditioner units. Your air conditioners won't work properly, if at all, if my opinion is correct.
Check the installation documentation of your a/cond model to find out the maximum distance between the Indoor/Outdoor units and only proceed if it is within the distance. If not, please redesign your layout.

140ft is kinda long, make sure they do a proper vacuum and recharge refrigerant.

Would you be happy if I said the cost is cheap and you got a good deal? What about I said it is expensive and that you got conned?

The fact is the installation is completed and you have already paid. Move on with your life and don't revisit the past that is already done.