Sync eBay and Delcampe stores

I need to sync my eBay store listings with my Delcampe store using the eBay API and the Delcampe API provided by these sites.

Initial Project:
- All my existing and new eBay store listings to sync to my Delcampe store.
- Sales on eBay to close the Delcampe listings.
- Sales on Delcampe to close the eBay listings.
- Changes (price, title, description, image) to my eBay store listings to sync to my Delcampe store.
NB: All listings have quantity of 1.

I have an opencart (version 1.5.6.4) store that I manage (and already syncs with my eBay store) here: https://www.koalastamps.com

My eBay Store:
https://www.ebay.com.au/str/koalastamps

My Delcampe store (currently empty):
https://www.delcampe.net/en_GB/collectables/store/koalastamps

Later there will be further features to add once the initial project is up and running. (such as sync my Delcampe and Hipstamp store sales to my website, log all Delcampe and Hipstamp orders and product sales to my website).

If interested, can you propose your solution in detail and price.

Thanks,
Rod