My understanding is that the stock SAS trucks (ie '85) are not that great off-road. It is only with the addition of several parts that they become a really big advantage off road. This is why it would cost you $3,000 to do your current IFS truck and make is SAS correctly. So this puts you in a $1,500 SAS truck with $1500 in parts to make it work as well as yours with $3,000 worth of work.

If you only have $3,000 to spend, spend it on your current truck.

My opinion: Put a few dollars into your current IFS, wheel it and save your money to buy something when you can spend more than $3,000. BTW the wheelbase it a bigger limitation on your truck than the IFS will ever be.