Ah, the vicious cycle of chemical gardening. You fork out money for fertilizer which in turn produces a weak plant that cannot resist the many diseases and pests that are waiting for an opportunity to take over. You invest more money to fume, spray and douse it in an effort to combat these plagues. Then, when you finally manage to get a harvest you have to pay even more money to remove them.
I'm afraid I don't have a short term solution to the problem. All I know is when I switched my gardening method to one that focused on feeding the soil rather than the plants my pest and disease problems over time greatly diminished. Now the few problems I have can be managed by using physical barriors such as row covers. I also learned to accept the few blemishes bugs caused on my fruit and vegitables.
Some of the books that helped me were:
Straight ahead Organic by shepherd Ogden
The new Organic Grower by Eliot Coleman
Also , you can search the Mother Earth News websites for all kinds of free info.
This is the Cheapest way I know to help you.It's not a quick fix but it's more sustainable and healthier in the long term.
By the way, organic gardening really does save you time in addition to money.