To use easels or not comes down a lot to each artist’s personal preference. Also it depends a lot on the type of artwork being produced. If you decide to use one or not I would like to emphasise the great importance of constantly reviewing your painting at an upright angle (as it would be displayed when finished). So often we are at a point with our painting when we are not very happy about how it’s going (know that feeling?). Putting it an upright angle and viewing it from a reasonable distance so often helps us to see where we need to go next with the painting and the areas that need improving.
Table-easels give an excellent support to a canvas or painting board. Many come with a mechanism so that the angle can be changed to suit the individual artist. There are many available that are light weight and portable. They are produced in a range of materials, ranging from plastic to metal to wood. You can also obtain more elaborate designs that are combined with a storage box.
Some artists much prefer the floor standing variety. These are great if you prefer working standing up. This obviously helps and encourages the stepping back and looking at the painting as it progresses. There is a whole range of floor standing easels made from different materials and so obviously ranging in weight and portability. One artist I know has an excellent metal floor-standing-easel. The legs are so telescopic that it can be turned into a table-easel very easily.
All good art suppliers, be they shops or online companies sell a good range of different models. The price depends on the quality and choice of manufacturer.
Personally I think this is an item that is better selected where you can test them. Art materials shows are an excellent place to choose easels.