Prozorro

Prozorro has an API - https://prozorro.gov.ua/openprocurement Judging by the description, you can do everything plus or minus as you ask. If you need an estimate for: to place a new tender, from Boxing it is transferred to Prozorro - receiving in OneBox all changes (not only new proposals) for tender proposals - I would be guided by 40-60 hours + the client will need to provide his access to the developers, because in the process with such APIs there are a lot of unforeseen problems, the API is in an unstable state and it clearly says "everything is under development". Essentially here is a step by step guide for developers - https://prozorro-api-docs.readthedocs.io/uk/latest/tendering/tutorial.html#tutorial