Does the prettiness of your website effect customers perception of your prices. In short yes.
This thinking goes against every tissue of my fibre, but seeing it in reality, its interesting that sites which are less design orientated have a huge following and enviable conversion rates.
An example of this was in my previous role where an xml partner had large booking figures and looked like it had been designed by your 5 year old nephew. http://www.smoothhound.co.uk/
Couple of article's that cover the main points: