I assume that any good GM clears a budget with the ownership prior to the draft and then works within that budget. Based on just last year and this year, it looks like the Lerners are more likely to care about an overall budget than something like a "total budget besides the first round pick". Hence, last year we had more signability picks due to Rizzo understanding that Strasburg was going to take up a lot of the budget. This year, we had more overslot picks because Rizzo thought (rightly, it turned out) that Harper wasn't going to cost nearly as much as Strasburg.
However, both years the end result is the Lerners spending in the top 5 among all franchises in overall draft signings, nearly $20 million last year and $15+ this year in total, which is a very good thing and something that hopefully will continue.
