I'd like to offer my fellow travellers some tips to help them booking balconies and to avoid any difficulties. If you'd like to add to any of the tips, please add on.
My suggestions are based on more than three negative experiences with Pamplona Posse, whom I would not recommend.
Booking a space is usually presented by 'per person'. The prices from my research can range from 75 euros to 95 euros on average.
SPACE ON THE BALCONY:
Sometimes some companies can pile way too many people on a balcony. The balconies are pretty small, and with three people, that is a pretty good amount of space. 4 people can start to get a little tight for a good view, and more than 4 people may be too much for the average balcony. So be careful to ask how many people they are booking on your balcony.
WHICH STREET TO BOOK ON:
I would suggest a high balcony on Estafeta, because its a longer route and you can see a further distance.
The Curve is on Mercaderes leading into Estafeta. If you can get a balcony at 'The Curve' on Mercaderes facing Estafeta, that's also a good balcony. The remaining balconies are shorter avenues of the run.
Lower is nice because you're closer to the action and excitement, but higher up is better because you can see a further distance.
GET A TOUR:
I would advise you to have the company give you a tour to show you your balcony doors ahead of time. The doors are not very prominent and kind of blend in. Companies don't tend to post signs letting you know that's the entrance to the balcony. Last thing you want to do is look for your door down a noisy crowded street in a foreign country :)
I had more than three occassions with Pamplona Posse where I met a locked door when I arrived at the time they told me to show up, and at the very same doors they showed me on the tour, and of course on the right days as I had my tickets each time. Ensure you ask your company what plan they have in place to ensure someone is available to open the door. Is someone waiting at the door until all customers arrive or are they waiting to be buzzed up?
Three times I had to get in to the building by sneaking in when someone else happened to walk out the building. The individuals meant to open the door were actually sleeping. So ask your company what Plan B they might have in case no one is there to let you in, or if you are buzzing and no one is answering. Ask them what their refund policy is in such cases. Hope you all didn't have the struggle I did to enjoy the bull run each morning!
Hope this helps!