How much does the price of a book influence sales?

I know I've covered this subject recently but it's still one that I've not quite fathomed. At the end of every month I list the individual sales of books and can then see which titles are selling well and which ones are lagging behind.

I noticed that most of my full-length regencies priced at £1.99 had sold only a handful of copies in May, whereas the ones priced at 77 p and 99 p had sold hundreds, and in some cases thousands.

Out 20th June £0.77

Although I still think longer books should be more expensive than shorter ones, I'm worried that ten of my titles are failing to attract readers. Therefore I've taken the decision to reduce the price of these books to 99 p for a month and will see if that makes any difference.
I have several writer friends who price all their books at 99 p regardless of length and others who price them all at £1.99. I still have my 30,000 word novellas at the lowest price of 77 p and I must say these seem to sell in thousands rather than hundreds.
I'm wondering if it's becoming harder to sell  Regency titles because there are so many new indie published writers joining an already crowded market.
I've been reading on other blogs that indie-publishers, with no previous publishing history, have sold 65,000+ ebooks this year – that's a lot of readers and very impressive. Most of these writers are writing contemporary romance and crime, which I think are the most popular genres at the moment.
My World War II books, especially the Barbara's War series, continue to attract readers and they are priced at £1.99. I'm assuming that family sagas have a different readership to a frothy, light-hearted Regency romance.
What do you think? Do you only buy books that are under a certain price regardless of the author?