[RickM]

$10k to $15k seems like the cost of one project, not three. Are you planning to do yourself?

As far as insulation you may be able to augment the existing material with the confetti type (treated paper product) insulation. Home Depot sells the stuff by the bale and you can rent the blower as well.

If your house has a ridge vent then be careful investing in a whole house/gable fan. The air that the fan pulls will be through the ridge vent and not from/through the house. An attic fan that resides in your ceiling will fare much better. I'd also add natural or thermosatically controled roof/vent fans as well.