"Pull" it over to GoDaddy from Dotster ... at your normal registration/renewal (one year extension) price at GoDaddy. This is NOT what would be considered a "free push" - those occur within the SAME Registrar.
Righto, he/she (the Buyer) will have to initiate the "pull" over to their GoDaddy account (you will get the confirming/authorizing E-mail from Dotster to "release"/approve it). They will also incur the GoDaddy one-year renewal cost ... so that money aspect may have played in to the initial negotiations of the sale.
At least make them aware that this cost will be part of the deal - full disclosure. This is a classic "pull" scenario, very common!
Congratulations on your first domain name sale, Suthra. :tu:
-Jeff