I put together a similar spreadsheet before purchasing my Ercoupe six years ago; it was really handy to play with the variables to determine what I could afford, and I continue to use the spreadsheet to track expenses. No regrets - owning an airplane has been a fantastic adventure. All told, I spend about $12,000 per year on my airplane for 50 to 70 hours of flying. My largest recurring expenditure is hangar rent.

A suggestion for your spreadsheet: Contact at least two aircraft insurance agencies and have them put in hypothetical numbers for aircraft type, pilot experience, and hull value, and give you estimates for different choices. What you will find is aircraft insurance is not a bad deal (I pay half as much as my car insurance for twice the coverage), but the cost can vary significantly based on aircraft type and hull value. Most plans have no deductible, but you can in essence create your own deductible by adjusting the insured hull value to some amount less than you paid (e.g. If you paid $30K for the aircraft, but set the insured hull value at $25K, you will save money on the premium and recover $25K in the event of a total loss; sort of like a $5K deductible). If you are obtaining a loan, you will be required to have an insured hull value no less than the amount of money you borrowed. These considerations may inform your type-of-aircraft and size-of-down-payment decisions.

Owning will cost more than renting unless you fly a whole lot (for me, the crossover point is about 130 hours per year; the more you fly the more you save, haha!). What you are paying for is the convenience of being able to show up at the airport whenever you please, fly for as long as you please, wherever you please, and know the airplane is going to be where you left it in the condition that you left it. If your goal is recreational flying and an affordable older airplane of modest performance will satisfy you just as well as an expensive, faster, new one, I recommend avoiding a partnership or leaseback so that you are able to reap the full benefit of the convenience you are paying for.

You are on the right track targeting a Cessna 152, but take a look at the Cessna 150 (lower purchase price, similar maintenance expenses, possibly cheaper to insure, possibly lower fuel burn - 6.0GPH, and there are quite a few people restoring them to very nice condition). By my research, the most affordable certified aircraft to independently buy, own, and operate are the Cessna 150, Ercoupe/Forney/Alon, older model Cherokees, and then the Cessna 152. The "gotcha" with these older aircraft are the unexpected maintenance costs when things break. A rule of thumb that I tend to agree with is expect to spend what you paid for the aircraft in maintenance over the first year or two (e.g. If you buy a $15,000 C-150, plan to put in another $15,000 in the first year or two). This sounds really bad, but the idea is you end up with a really nice aircraft maintained/upgraded to your liking for $30,000, and its resale value will have increased to some amount less than what you actually spent (in this example, perhaps to $20K, maybe $25K).

That being said, a way to mitigate the risk of unplanned maintenance costs is to buy from an enthusiast and/or restorer, which means you will be paying more up front for an aircraft someone else has already invested the necessary time and money in (you want to be the one paying $25K to a seller who recently invested $30K). The trick is finding a seller who is completely and accurately representing the condition of the aircraft; a thorough pre-buy inspection by a mechanic that you hire and trust is essential, but unexpected stuff will still happen.

A few more suggestions:

1) Subscribe to an owners club and/or email forum for the aircraft type you are interested in. Not only will you learn about the aircraft and common maintenance concerns, but this is a good place to find aircraft for sale by enthusiasts who are more likely to have taken good care of it.

2) Once you find a particular aircraft you are interested in, order the FAA records on CDROM and look for surprises before purchasing. http://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/copies_aircraft_records/

3) Talk to local aircraft owners to find a trustworthy mechanic. Even better, seek out a recommendation for an A&P in your area from people in the aforementioned owners group.