what's the exact reimbursement process/amount?
They promice even 70% reimbursement
On this website (in Polish only) you can find all of information regarding conversion for "BIO" - environment friendly heating system in Wrocław and application for money compensation.
Regarding the cost of the entire project let me quote (and google translate) another website (read - many useful informations)Changing the coal boiler to another does not require substantial modifications to the installation, just as replacing it with a heating node. Therefore, these investments are relatively easy to carry out at a reasonable price - in the case of a detached house it is several thousand zlotys (excluding subsidies). The gas boiler itself up to 28 kW can be bought for 3,000. zł, although better models are even more than twice as expensive. You still have to pay for the acid resistant flue pipe, labor and processing of the installation in the boiler room, and if there is no gas connection - also for its implementation.