which database should I use?

I would like to have a database that:
• stores all the property addresses and names in all counties in only a single state, so efficiency is a factor.
• allows for multiple people to access the database at the same time and make changes to it.
• is installed on multiple computers, so price is a factor
• has a relatively small learning curve
• is compatible with excel, since a lot of calculations to manipulate strings (e.g. addresses) is necessary before info is imported into database, UNLESS the database has similar functions like excel to manipulate content, such as splitting addresses based on spaces or delimiters and being able to compare and match two files of content and do something if there's a match
• has the ability to import columns from excel and translate them into fields, if the fields do not exist, and if they do, then to update the value of the fields
• has some kind of ability to measure success of a marketing campaign

Does anyone know of a database that best suits these needs?

Thanks for response.

I think it's about how you design db and data loading process, no matter use which rdbms.

Correct, designing something in PHP which already exists in the Access GUI will take longer than getting a copy of Access. However, is a PHP/MySQL that much more efficient than Access/Ace as I hear? I was hoping someone would do some kind of comparison between the two.

You should start with MS Access, because is more easy and is very potent for a small or big business. Also, if you lost a data, Access is easier recover than others services.