Acoustic bands are a great choice for different types of events due to their adaptability and excellent entertainment due to usually large repertoires. From solo acoustic artists up to 4 and 5 piece bands with Mumford style folk pop bands very much in favour.
An acoustic duo would normally consist of a vocalist and acoustic guitar and are ideal for more intimate events like a drinks reception. A three piece option would be similar but would include a Cajon which is a box percussion instrument.
Mumford style folk bands would include acoustic guitars and upright bass and are ideal for festival style events.
Also you could choose roaming bands these are usually acoustic bands roving amongst the guests at outdoor events encouraging everyone to join in singing and dancing and perform unamplified, so no need for set up times. A Mexican mariachi band would be an example of this style of bands which would consist of 2 x acoustic guitars and trumpet.
Acoustic bands are ideal for venues that have sound limiters in place and bands can only perform at a certain level in some cases with no amplification at all. Always check your venue for this before booking an event.
As for space for an acoustic duo for an indoor event the rule of thumb is generally 3×2 meters and 4x3m for a four piece band.
Prices do vary on each type of event but for acoustic solo artists prices would start from £250 and an acoustic duo would start from around £450 and four and five piece Mumford style bands around £1500.
These are just a few possibilities for an acoustic band or artist.