I have used SellerEngine Plus for many years (from the same people who offer Sellery, which is too steep for me). It does everything I need for about $50 a month. It is a Software as Service program that resides on your computer and churns through repricing calculations at an pretty good clip. I typically reprice around 1,200 items in less than ten minutes, pretty much around the clock. Customer service is excellent.
Decisions can be made on a wide variety of parameters, including both New and Used current prices, popularity, number of sellers, ratings of sellers, your COGS, etc, etc, etc. You can set maximum and minimum prices for each item. Minimum pricing is important to avoid the “race to a penny” and to lessen the chances of a bad mistake being made – like unwittingly losing money on a sale. With a bit of practice, you can replicate just about any set of “rules” you would have used if you were doing it yourself.
Having said that, there are some real issues you need to understand and take into account.
SellerEngine, like most repricers, relies on the Amazon data feed. In busy and highly competitive categories like books, CDs and DVDs (where I sell), the Amazon data feed is incomplete and can lead to some VERY misleading pricing decisions. This comes about from the fact that Amazon reports only a limited number of results for each item. If there are too many results, Amazon will throw out a few. Ugh!
So, you will find that you need to be very creative in determining ways to estimate what the real used prices are from the partial data you are presented. It takes some squinting, but you can learn to guess close enough to be competitive.
I would most strongly recommend that before using a repricer you examine how prices are determined on Amazon. What does it take to win the Buy Box? (Yes, I know the formula for that is a secret, but by observing a number of listings in your categories, you can get a pretty good idea of what it will take to share the Buy Box.) How do prices of Used items compare with the prices for the same item in New condition? Etc, etc, etc.
And after you begin using a repricer, I recommend that you examine each actual sale you make and determine whether it was sold at a reasonable price or not. This will build your confidence in the system.
Seller Engine offers a free trial, so download it and play with it. You can run all manner of scenarios without actually telling it to upload the calculated price changes to Amazon. When you are satisfied, then out it in automatic and let it rip.