If the fan does not come on, definately fix that first. If that is the problem I am sure you can remain within a budget. It is probably just a relay or thermal switch. I do think that the fan should come on early with the AC on. You do need to make sure it does come on with the AC. If you do not keep the condensor cool the pressures in the system can get high and damage the AC components.

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1995 G320
1984 280GE
1971 Unimog 416