Can I still purchase Quartus 2 Subscription 13.0sp1? Does DSP Builder license comes with the subscription?

1) License are backwards compatible for Quartus, you can purchase the license and use the old version of Quartus.

2) nope, you can refer to https://www.intel.com/content/www/us/en/programmable/support/support-resources/download/licensing/overview.html

subscription got include some free IP https://www.intel.com/content/www/us/en/programmable/products/intellectual-property/design/ip-base-suite.html

But not DSP.