The approximate amount of donation varies depending on which path one takes.
One way is to donate for auditing and participate in auditing services all the way to Clear. The preferred route, however, is to train as an auditor and co-audit with another Scientologist. The co-auditing route requires far less in donations and one gains tremendous satisfaction in helping another attain the state of Clear. As auditing costs much more for the Church to provide (necessitating several staff for each parishioner) donations are naturally higher. Training, then, is far more economical, which acts as an incentive for persons to train and then co-audit, without cost, to the state of Clear.
No matter the path one chooses, however, all who attain the state of Clear express the pricelessness of greater spiritual freedom.