Direct buses might be difficult... But there will be many buses from Srikalahasti BYPASS to Gudur BYPASS.. Bypass in the sense reach out to connecting Highway NH71 kalahasti entrance...
There will be many ONT buses coming from Bengaluru to Nellore/Ongole/Bza Everyday.. GDR BYPASS stop to GDR railway station is around 3km and Many autos will be available..
P.S....
more... Currently NH71 RU-NYP Highway is heavily congested due to renovation.. plan your travel in advance