HAN/REP is not a cheap flight, often $200 for that leg alone. If you're getting SGN/HAN and HAN/REP for $240, that sounds pretty average to me. SGN/HAN though can often be booked for $25-$50, depending on date, time etc. if you want to book it separate. I agree VN is superior to Vietjet, but Vietjet I fly once in awhile, and Jetstar I don't fly. Remember also not to just rely on an aggregator, as the VN promo fares don't always show up, so check the VN website directly (imo). Early morning flights are more likely to be on time than later in the day.