You could get the 2 zone tageskarte for €8 which allows you to go as far as Pirna.
4 day tickets for Dresden wil cost you €20 as opposed to €19 for a weekly ticket (valid from first use). 4 day tickets including Pirna will cost €32 as opposed to €27 for a weekly ticket.
To excess a day/weekly ticket for Dresden to allow you to reach Pirna will cost €4 (€2 each way)
BTW, whilst I have been to Dresden, I haven't used the public transport, I just got this info from the website