I think it is important to be upfront with any financial barriers so your physiotherapist can work around it. You may speak with your therapist to see whether you may be provided with more exercises in the mid to later stages of the healing process.
The worst thing you can do is to book a treatment session and not show up, it is very disrespectful and your therapist is basically waiting for you when he or she can be seeing another client instead. Just be honest and see if there are any other alternatives such as less frequent visits or follow up by phone or email.