You can get cheaper freewheels on ebay like the shimano or dicta freewheel, but they are not very safe for trials usage, once you get validated on here you should be able to get a second hand one for a reasonable price.
Just looked at your pics and your bike doesnt have any chain tugs, so unless you want to buy some you will need to move the wheel backwards in your frame until the chain is tensioned correctly. But make sure that you move the axle evenly on both side.