1. Convert website to wordpress
2. Modify WP plugins to work with existing CMS
3. Integrate wordpress into existing website
We are currently stuck with the first option for about a year - big volume of work, high cost, difficulties to recreate old URLs structure on Wordpress.
I wonder if Wordpress installation into sub-directory of our website can work... Basically we would like to keep old content as it is and continue with new content on Wordpress.
What could be the most time/cost/SERPs effective solution? Any advice will be appreciated.