You can try N30 in ang mo kio, been to the place, lot of finished tank and lead time still take 4 weeks, but the workmanship very good.
Alternatively you can make tank and sump only with no.3 kelantan road, no so pro, but very short lead time abt 5 days, they don do cabinet.
If you looking for standard tank like 3x1.5x2 with ios and sump and cabinet, aqua empire in pasir ris got ready unit at abt $1.4 estimated.