If you visit different sites, you may find different prices depending on the provider, but the biggest factor is the type of mail you are wanting to send. For example, the latest rate for sending a postcard is $0.34, so a $0.34 postage stamp will be enough. Sending a First Class Mail Letter will cost you $0.49, which means you will want to buy the “Forever 49-cents” postage stamps, and add $0.21 in stamps for every additional pound in your package. International shipping is, of course, more expensive; $1.15 for a letter, $14.73 and up for a package. There are also special stamps for Priority Mail Express which you will want to buy in case you want your mail delivered sooner; these stamps can cost up to $23.75.
Sometimes you may find yourself not being able to get a stamp of the exact amount you need for your mail. For this reason there are many different stamps with different prices which you can combine until you reach the needed amount: $0.01, $0.02, $0.03, $0.05, $0.10, $0.21, $0.34, $0.49, $0.60, $0.70, $0.91, $1.00, $1.15, $2.00, $5.00, $6.65, $10.00, and $23.75.
If you are looking to save some money or ship frequently, you can buy your stamps in formats that may save you numerous trips to the store. These formats are: blocks (4 to 10 stamps which cost from $1.36 and $3.40 respectively), sheets (formats and costs vary depending on the type of stamp but trend from $5.80 for a sheet of 12 stamps, $7.84 for 16, $9.80 for 20), rolls (100 stamps for $34.00 and up), coils (10,000 stamps for a minimum of $300.00 and going up to $4,900.00).
If you want to buy stamps in bulk from Amazon you should be careful because many sellers tend to raise their prices. Always check the USPS website first and compare different prices to find the lowest one.