Britney Spears -- I Got A New Vegas Deal ... I Make Celine Money Now!

Britney Spears was doing well with her Vegas contract -- raking in nearly $30 mil for 2 years ... but we just found out, 50 shows into her run, her show was so successful she got an even sweeter deal.

Sources connected to Britney tell TMZ ... the singer did indeed sign a contract for $310K per performance, and with 96 concerts over 2 years the total was $29,760,000.

But Planet Hollywood was blown away by ticket sales, which they said broke Vegas records. So Britney's people went back to the bargaining table and hashed out an amendment -- with back end, merchandising and other perks, the singer will earn around $475,000 a show. Celine Dion, the top money earner in Vegas, makes $476K a show.

Planet Hollywood actually added shows for Britney ... she'll now do 140 shows during the 2-year residency.

Bottom line ... with all her ventures ... we're told EVERY WEEK, Britney's people deposit around 1 MILLION DOLLARS in her bank account.