Terry,
A sage friend of mine once said that you should bank 25% of your budget rather than use it on the purchase - you'll use it in the first year on maintenance.
It was perfect advice for the three airplanes I've owned - even with careful pre-buys.
Best regards,
Rick
I think this is nice advice as long as it doesn't mean you can only afford a "cheap" 150. Go cheap and you are more likely to need that 25% and a whole lot more! If this is the case you are better off setting aside more dollars before you get into the joys of airplane ownership.