In between XE and EE there is SE <i>and</i> SE1
Note to self: I talk about Oracle XE (sorry, "Oracle Database 10g Express Edition") a lot because it has become extremely popular. It also installs easily and quickly enough to do during a demonstration. The perception is that there is free Oracle XE and something else that costs a lot. This is just not true. We have various editions and our "Standard Edition 1" is actually relatively cheap: the SE1 home page says "$149 per user (5 user minimum)" (at the time of my writing this). Of course PHP works equally well against SE1 and the other editions of the Oracle Database, since the Oracle code base is the same across the set of XE, SE1, SE and EE.
This is the product matrix of the Oracle Database Product Family (PDF)