In Need of Price Book Ideas!

So I'm getting my couponing under way pretty well, but there's one important aspect I have yet to tackle.  A price book!  Say I see something on sale at store A and something on sale at store B and the same item can be found at a low price store.  How can I know which price is the best?  Sometimes the low price store's every day price can be lower than the sale prices at store A or store B, sometimes store A or B has it for a steal with double coupons and sometimes store A does not double coupons, but will match competitor's prices.  

How can I know which deal is the best if I don't track the costs at each store?  Clearly I need to develop a price book.  I've read various methods.  Some people use good old fashioned notebook and write down the prices they paid as they go along.  Some people use aps on their computers or smart phones and some people have completely different methods.

Ok, so I'm an old fashioned kinda girl in many respects, but I'm a tech-y kinda girl too, so the idea of keeping track of prices electronically through a spreadsheet of some sort is appealing to me.  A bonus would be to have an app that you can use on your computer and smart phone both that syncs with each other.

Any ideas for me to try?  I'd really appreciate any input! I have a number of receipts collected from shopping trips and need to get the prices in a price book of some kind soon.

Please comment!!

Thanks! :)