We have 2 "in and out" cats that we treat 6 months of the year with Advantix. It's not cheap but it has worked for us for the past 15 years. Much cheaper than trying to get rid of fleas!
Be careful with spray bombs. I got one at the vet's 30 years ago - followed instructions, kept cat out of house for 3 days - still poisoned him. I have never gotten over that.