Nagendra presented a Valmiki statue to Gandhi on the stage after he was welcomed into the Congress party.
"The gold-coated statue cost Rs 60 lakh," Nagendra told reporters.
Alongwith Nagendra, BJP MLA from Vijaynagar B S Anand Singh also formally joined the party at the rally.
The BJP in a series of tweets, has come down on Gandhi and Chief Minister Siddaramaiah for inducting Nagendra and Singh, who are facing charges of illegal mining.
"Dear 10 per cent CM Siddaramaiah,I would like to remind you, your padayatre in 2013 about the mining sector. Now, inducting Anand Singh into the Congress camp has only proved you are a corrupt opportunist. Case of amnesia," he tweeted.