First I suggest that you go through this comprehensive trouble shooting document and see if you can optimize the performance of your MBP as is is currently configured. The monetary outlay will be zero.
If you look at the Crucial web site, you should be able to install 8GB RAM and a 240 GB SSD for $282.
Personally, I would install the RAM first and see if that makes a meaningful difference. Install the SSD only as a last resort. I have an antipathy towards SSDs based mainly on cost. Others have different opinions.
Also update your OS to 10.6.8.
Do not be seduced by quad core CPUs. They will perform faster only if the application is designed to take advantage of all cores. Most applications are not (at least the older ones).