Taylor Swift's not the only person making big money while performing ... 'cause even a T-Swift impersonator is raking in the dough -- saying she makes nearly $20K per performance. Olivia Mojica -- a singer who shares starkly similar features to the pop star, and leads the "Blank Space Tribute Band" -- stopped by TMZ's "Swift-Tea Podcast" Thursday ... telling us she actually quit her day job because she's making so much tributing Swift.