Baggage is where the cheap ticket often stops being cheap. Allowances depend on the airline and the fare you bought — not on where you are flying — and the gap between adding a bag online and buying one at the counter is usually large enough to wipe out whatever you saved choosing the cheaper airline.
What your allowance actually depends on
Two passengers on the same flight can have completely different allowances. Full-service carriers usually include checked baggage in the fare; low-cost airlines sell it separately, and the cheapest fare class on a full-service airline may include less than you expect. Read the allowance on the specific fare before comparing prices, not after.
Weight limits also come in two shapes. Some airlines give you a total weight; others give you a number of pieces, each with its own cap. On a piece-based allowance, one overweight bag can be charged even when your total is within what a weight-based airline would have allowed for free.
Two tickets means two separate allowances
If your journey is on two separate tickets — common when connecting through Doha, Dubai or Kuala Lumpur on different airlines — the allowances do not carry across. Each ticket has its own, and you may have to collect your bags at the connecting airport and check in again, paying that airline's excess rate if you are over.
On a single through-ticket, the allowance for the whole journey is generally set by the first airline, and your bags are usually checked all the way to Kathmandu. That is worth something beyond convenience: it is one fewer place for the trip to go wrong.
When cargo beats paying the airline
For heavy items that are not urgent, sending a box as cargo is often cheaper per kilo than airline excess baggage, particularly from the Gulf and Malaysia where the freight routes to Kathmandu are well established. The trade-off is time and paperwork: cargo takes days to weeks, needs customs clearance at the Kathmandu end, and someone has to collect it.
Do the comparison on total landed cost, including clearance and collection, not on the shipping quote alone. And confirm what you are allowed to send: rules on electronics, batteries, liquids and quantities differ between carriers and can differ from what you may simply carry in a suitcase.