The draft is set up in such a way that only a very few players have what one could fairly call "bargaining power," but generally yes.
To illustrate, in the tenth round of this year's draft, the median bonus of college juniors (including redshirt juniors) was $125,000. The median bonus for college seniors in the same round was $10,000.
However, there are lots of other baseball and business variables at play that can affect the bonus greatly, as shown by the circumstance that one junior got only $25K while a senior drafted later in the same round got $138K.
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