Each year I go to one of these Pre Edinburgh festival shows at Bar One in Derby. They have 6 acts on starting at 2pm and lasting until around 10pm. They are all professional acts and are basically trying out new material for their Edinburgh Gigs. The price of £7 for the full day is therefore excellent value as you could pay that to see one act. Some of the material might not be to your tastes but a new act comes along every hour or so meaning you should see something you like.
I will be at the venue at 2 pm and will be catching the train at Notts Station at 13.10 and getting the return at 22.18 so it's quite a marathon. Around 10 people came last year and everybody enjoyed the day. You are of course free to come for as long or short a time as you like. You get a stamp on entry and may leave and come back as you wish.
The Venue has a nice, comfy outdoor stage area and serves simple but effective /cheap food most of the day. It is usually busy but not very crowded and the beer is ok and reasonably priced. Therefore although it's all day it shouldn't break the bank.
You may book in advance on the link or you can usually pay on the day.
Details of the acts on