I had a campaign a few months ago where all my ads were on the first page for my industry. I recently scrapped that and started a new camapign where instead of £3+ CPC I'm now paying only 5 pence. Most of my ads now fall on pages 2-4.
Amazingly, with a few more keywords and a bit of fine tuning I'm now getting the same conversion rates I used to but with an my overall spend reduced by 98%!
You can actually get a recommended budget for a campaign within AdWords.
All the estimates and advice go by the wayside as a campaign takes on a life of its own. You may end up tweaking a dollars-per-day campaign to elegant perfection, or you may end up spending thousands per day via brute force. Like most things in life, it is what you make it.
quick start:
Step 1: determine your overall revenue per visitor, if available.
Step 2: enter conservative bid per click and budget per campaign.
Step 3: create a variety of advertisements and keyword phrases.
Step 4: compare adwords performance and site conversion stats.
Step 5: if favorable, up the ante. more words, higher bids.
Step 6: test, analyze, react, repeat
If you want to compete against 'web design' or 'free email', then you are going to have to pay a lot of money. Just find the rarer terms that people search for and advertise on them.
Alternatively, and I find myself doing this sometimes: people search and by the time they get to page three and nothing is relevant, they start to wonder if the paid adverts are any better. I know I do, but I start to look at the adverts on the right-hand side, but I do not go back to page one. I just start looking when I think the free results are not giving me good enough results. So being low on AdWords does not matter as much as people think, as long as you keep your CTR up and the adverts active.