Centaurus,
You may well be able to get a 737 type rating for the same outlay as the agricultural rating. However, by that time you will also have outlayed for an instrument rating, possibly an instructor rating, an ATPL, and you can't expect to make the same return on that far greater outlay as the ag pilot's earlier and far higher return.
Thankfully, CASA have granted a dispensation for the operation of 802,s and Dromaders at weights exceeding 5,700kg as the ATPL course bares little relevance to their operation. That, however, doesn't mean that any old punter will find themselves in the seat of an 802. Only about half of the contenders that find employment as loader/mixers will continue on to ag flying positions. Much less than half of those will pregress to the seat of an 802.
Today there are far fewer ag aircraft being operated in 1st world countries due to the characteristic of the large hopper capacity and wide swath width being an unbeatable formula for operational efficiency. Therefore there are less seats available and far less ag hours flown per year. This is not a contraction in the industry by any means. We will probably not see the busy days of the late 1990's again due to some technological cropping advancements and a far greater operational capacity to cover the work.
That equates to far greater advantage to those who reach the coveted seats of the world's increasing fleet of 800 gallon machines.