You mention that you can not afford mysql. If you are running your own server, you can download mysql for free from http://www.mysql.com If you are renting space from a provider, most of the ones I have seen charge $5-10/month if that much for a database. The performance gains are exponetially positve for large databases.

"The social dynamics of the net are a direct consequence of the fact that nobody has yet developed a Remote Strangulation Protocol." -- Larry Wall