Flying 30-40 hours a week till you fulfill the requirement?
You are at 250 now and need 1500 which means you'll need to fly 1250 hours.
I don't remember reading if you were the going to be the only guy flying this aircraft, if your not, multiply the below times by two at a minimum..
It sounds like you are the "sole-operator" of a single C-150, if you could fly 40 hours a week, that's over 31 weeks of flying at 40 hours a week.
I can tell you from experience, while it is very possible to fly 40 hours a week, but weather, maintenance, (scheduled or unscheduled) happen which makes flying 40 hours a week an unlikely event.
The aircraft will need oil changes, parts repair replacement, possibly and engine overhaul if your putting 1250 hours on it, depending on how many hours the engine has now, tire changes, etc...also, you will want some kind of insurance to cover you for an accident.

Also, are you going to fly the same routes around home, or are you truly going cross country? where will you stay? hotels and eating out all the time is expensive and adds to the cost. I read somewhere in here that the dry rate plus fuel adds up to over 50 grand!...

All of these items I promise will stretch your 40 hours per week to a more conservative average of about 20-25 hours per week. (you'll want a day off eventually, try flying 6 to 7 hours a day in a C150, it hurts! ask an instructor how it feels!)

Planes break, people get sick, parts take time to ship, owners sell off their planes, planes get damaged in storm, ...
The 31 weeks will probably be closer to 50 weeks at 25 hours per week (1250/25=50)
I hope if you chose this route that you have some form of contract with the owner and they are in it for the long haul?

IF you have 50K (if you have 10K?) sitting around somewhere go back to flight school and get your CFII-MEI and GET PAID TO FLY THOSE 1250 HOURS! (not yelling, just emphasizing) OR if you have 50K, go out and buy a used C150. They can be had for 12K-15K with reasonable times left on the engines. Find one with descent time left on the engine, fly it to TBO then sell it for 8 or 9 thousand and recoup some of the cost?