Cost of massage in Luang Prabang

Massage prices vary a lot in Luang Prabang from very cheap to very expensive, ranging from as low as 40,000 LAK ($5USD) for a 1-hour massage, to $50-80 for a 1.5-3 hour spa package
30 minutes, 1 hour, and 1.5 hours are the most frequently offered massage durations, but many fancy spas will usually offer you >2 hour spa packages
The absolute cheapest massage you can get in Luang Prabang is 40,000-50,000 LAK per hour ($5-6USD). The Red Cross, for example, runs this massage shop that's price point. These will be very "no frills" service

The typical mid-range massage place will cost 60,000 LAK ($7USD/h) for 1 hour of traditional massage. For these services, you simply go in, get your massage, and leave. You usually don't get your own room, but rather the massage is done on a bed in a shared space
These mid-range places will usually also have some fancier packages too, like aromatherapy/oil massage. These services will be more expensive, costing about double what the traditional massage. A common price point is 145,000 ($17USD) LAK for 1h or 220,000 LAK ($26) for 1.5 hours of service
Many of these places will also let you use their sauna for 15,000 LAK. But don't expect any other facilities
You don't usually need to make reservations for these types of places. Just walk around town and you will find lots of these massage shops where you can just walk in
This is what a typical mid-range massage place looks like:

Beyond the mid range places that most visitors go to, there are also a handful of very high end end ones.
These are often attached to hotels or run by professional spa companies, and they offer not just the massage but full service spa pacakges.
Places like Burasari, Sofitel le Spa, Palm Tree are all rated very well on Tripadvisor. Their prices are very expensive, starting at 450,000 LAK per hour ($50USD/h), plus 20% in taxes and service fees.
Of course, what you get for this price is private room, relaxing ambiance, professional masseurs, and full access to their spa facilities including shower and pool. These places usually require reservation so it's best to book through their website or call them
This is what a high end one looks like (picture is of Burasari):

Tipping is not expected. But if you really want to, 5000-10,000 LAK is enough. Also, at the super high end places, services charge is usually added to your bill so there's absolutely no need to add anything extra

Let me add a related brief