you will likely never see a 128gb ide ssd mainstream (cheap) because ssd's are mostly sata, although you can use a sata to ide converter...i have used on on my apple tv and it worked to add a 500gb drive into it.
if you cant fit it in let me know...i can design you a connector/converter for it.
This isn't about my budget. I think it's it's time for you to get a new Mac instead of upgrading a very old Mac for the same price.
I sell my Mac every 18 months or so, depending on when they refresh the line to my liking. I always buy right after an announcement as well. Selling my Mac affords me the ability to only pay between $300 and $600 for a brand new Mac. It has worked really well for me over the past 5 years or so - I will definitely continue.