The problem with your plan is neither the cost nor the reason for doing it, nothing wrong with honorably trying to meet the ATP mins this way. But what you are missing is all the stuff one learns by taking the standard time building routes available, such as teaching and performing aerial applications for a couple of years. The ATP mins for first officers were set that high not to get people to rent more Cessna 152 block hours, they were set that high to get people who need a variety of professional flight experiences to get that experience somehow and not to jump from 250 hours into right seat of an airliner with so little knowledge. You need that experience. Working with passengers, going all over the IFR system, flying twins and other aircraft such as tailwheels, working for bosses, working with students, I could go on but there is a lot to learn and you will miss all of it logging a thousand hours in a hobby airplane flying day VFR all the time in the local patch. In addition, any airline that is worth working for will see a thousand hours of shallow flight time in there and wonder how successful you will be flying a totally different job when you have so little variety in your aviation background.
Get your CFI, CFII, and MEI. Teach for a thousand hours. Get a load of that, then quit and fly Part 135 or do aerial applications for another year. It will be some of the best flying you ever do and make you a well rounded pilot. The case for buying time blocks is not to circumvent the FARs, or achieve minimal compliance, it is to learn more about what you plan to do for the paying public before you do it. Don't miss out on the opportunity.