Here are a few thoughts on bids. Over the years I have learned that you don't give one price. No, it is much better to give a low, and a high. If you feel like you need even more slush room, give a mid-price too. You can't just give prices though. I find the best bid follows this simple outline:
1) Restate what you understand the customer wants. This is great way to make sure you understood what they said, and guarantees you are both on the same page.
2) Explain what you are going to do for them. Don't get into the particulars yet. This is a 'I am smart and creative and this is how I think my awesomeness will translate into money for you'.
3) Now state what the heck you plan on giving them for their money. This is where you get very explicit. I call out each piece, and how many revisions, how many sketches I anticipate, color rounds, whatever... this is the place where they find out if they are buying the stock or the upgrade. If you are going with tiers, and options, you can break this down further to include the 'stock' price and the 'upgrade' price.
4) Do you have style samples or samples in general you want to show them? This is a great place to explain samples, and then I usually stick them on at the very end of the proposal on a separate page.
5) Tell them how much this is going to set them back. Refer back to section 3 to callout the pricing for any variations you are giving them.
6) Terms. Do NOT forget this part. This is your safety net. You can explain payment expectations, and time requirements to guarantee you can deliver on your promise.
Ta da! Really not a complicated process, nor difficult. Just time consuming to ponder and regurgitate.