Mil helo guy turned mil big wing FW guy.
I'm looking to be able to be hired at a LCC in a few years. I'm flying heavies right now but will still have under a 1000 hrs FW time after this tour. I'm considering buying a cheap GA plane (C150/2) to possibly build a couple hundred more hours to get me over the 1000+ hump. I'm not interested in flying banners, jump, or CFI type gigs on the side. Not seeking to jump straight to one of the top tier guys but would like to skip the regionals. Would these recreational hours be a waste of time in trying to get hired at a low-tier major/LCC?

“Heavy” what?

In the old days anyway 100 hours/year is about the break-even point between owning and renting. If you're going to do 200+ in well under a year the math might work out, but there's an obvious risk that you could end up on the hook for a VERY large MX bill if something big breaks... like more than the plane is worth. So I'd consider the risk of being out tens of thousands vs. saving a few grand.

It was not uncommon for folks to buy light twin, when you needed 300-500 ME to get a commuter job, but they generally sweated bullets on the Mx and unloaded the thing just as soon as they got the time they needed... twice as many expensive things to go wrong.

If you're otherwise competitive and just need to meet ATP mins, it might put you over the top, most civilians have plenty of ASEL time in their total. Probably need to understand what actual competitive mins are the airlines you're looking at (vice published mins). Also some ULCC are trying to avoid new-hires who are obviously in the competitive ballpark for big-six (they might like your helo time in that regard, but they might not like your mil FW).

I would see what’s available with rentals or a flying club near you. The fixed ownership, fuel, & maintenance costs will have you at least 1/2 the costs of a rental, lacking flexibility to get out. There is the partnership idea too.

With renting you can vary things some. At one time there were great flying clubs at many military bases, seem less common now. With aviation interest there is usually rental options near military bases.

I also don’t think burning holes with your C-152 is all that valuable of flight time, though it is flight time.

Have you checked out RTAG? There are some folks there who bought time builders and advertise deals for buying block time on their aircraft.

I owned a C150 with an auto gas STC. It really wasn't enough horsepower for going anywhere except in circles especially in the Rocky Mountains. A&Ps have told me to steer clear of an aircraft burning autogas because it causes more problems than its worth. If you use the STC absolutely make sure the gas has zero alcohol additive!!

The Cessna 152 has a little more horsepower but I would go with the Sparrowhawk with a 125 HP. If you live close to sea level the C150 should be fine. It's a rock solid airplane that will hold its value! Pre inspection purchase need to to check the firewall isn't bent and there is no corrosion. Look for a low to mid time engine. It's a trainer and folks don't keep the nose gear off the ground in the flare. Remember to make two landings, main gear then nose gear.

I think its a great idea to time build.

Agree with 155mm
Many folks then sell the aircraft for almost same price as they purchased. Can use that in your calculus on value of purchase.
Many pilots purchase these type aircraft (low cost Pipers, Cessnas, etc for their kids to build time and then sell to other pilots doing same LOL
Like cars stay local overseas form one service member to the next.
Good journeys