(harp)
There are essentially two different types of harps. Lever harps and pedal harps. Technically, there might be a third type of harp: the lap harp or travel harp. Basically, lever harps are for celtic music and pedal harps are for classical. Travel harps are essentially portable version of the lever harp, and some may not even have levers. Of course, that is probably over simplifying it, but the type of music that a person would want to play may factor into the decision of which harp to choose.
Levers can be used to changed an individual string to produce a different type of sound. A pedal is used to change multiple strings to produce a different type of sound. Bridge pins can help prevent the fingers from grazing a vibrating string while the harp is being played. Tuning pins essentially help hold the string in place. A full set of levers is recommended for those that want to play a wide range of music types.
In terms of cost, a travel harp will probably cost around $700 to $2,000. A lever harp will probably run in the $3,000 to $6,000 range. Finally, pedal harps are basically $10,000+ easy.
A set of strings themselves is cheap by comparison, being maybe only around $50 to $400 depending on what kind of harp you have, how many strings you have, and what type of string. However, repairs for harps can easily run into the thousands regardless of whether it is a lever harp or a pedal harp. Pedal harp maintenance can easily be several hundred.