My main caution here is that you will be astonished at the number of abilities in Oracle that MySQL does not support. Mainly these are things regarding database constraints and relational methods. No views, triggers, stored procedures, CHECK constraints, schema, domain, etc...
Now, if you are not using any of these in your Oracle DB, then it might not be so difficult to move to MySQL. But really, for a database of any complexity at all, these relational methods are lifesavers. If your database of 120,000 records is mission-critical in any way, I would recommend you think about this.
And, I would seriously recommend you consider one of the other open source database systems, which support more of the standard relational methods and constraints. The three I know of are as follows:
(very mature project, stemming from Berkeley research and Ingres)
(open source version of Interbase)
(open source version of SAP/Peoplesoft DB)
From what I have seen so far, PostgreSQL is the system that is most similar to Oracle, even supporting Schema and Domain, as well as most of the ANSI-standard SQL constructs. (MySQL's SQL deviates significantly from the ANSI standard) It will take a little more work to learn, but it really is a nice system.
As for a web-based system, PostgreSQL with PHP/Apache running on a Linux server, is a great combination, although PostgreSQL works well with most programming environments, including Windows-based clients, via ODBC and JDBC. At the moment PostgreSQL mainly requires a Linux/Unix server
, but there is a Beta available for running PostgreSQL natively on Windows servers.
To comment any more intelligently, I would need to know some more details about your software, and your server environment.