ACM is a fairly low cost product. It is sold on a "per head" cost of how many users you will have. ACM itself is essentially Windchill PDMLink with all the CAD management stuff removed. It allows checkin/checkout of versioned content, including compound documents which may be bursted automatically.
It is a more involved install than Arbortext Editor but not too bad these days. Note that you will need a database behind ACM, your options are Oracle or MS SQL Server. Database licence costs are separate and in addition to the cost the base ACM product.
ACM requires a bit of horsepower (depending on how many concurrent users you plan having). Therefore you will probably want to host ACM on a beefy server. In medium-to-large ACM deployments the database is also on a separate server from ACM.
Hope that helps.
