Both times I've had A/C fail, the failure itself evacuated all the refrigerant for me. Both times were under $300 fixes for me. Both repairs lasted until I replaced each of those cars.
Firstly, "all" the refrigerant doesn't actually leak out on failure. There's still going to be residual left in the system once the pressure differential is either equalized, or reduced to a level that the failed seal can manage.
Secondly, the OP's system still has all the refrigerant in it. He's stated that, while it's noisy, it's still cooling. That means it has refrigerant in it.
While I agree that the average home mechanic isn't very likely to get nasty letters from the EPA, shops are. And as a consequence, they'll always make sure to use a recovery system because, while the EPA can't watch every guy with a wrench in his home garage, it absolutely
does monitor shops. That's added cost for the shop that people who simply look at parts prices don't take into account.
Finally, it doesn't make a damn bit of difference what your past repairs cost because they aren't the same. The price online for a new, OEM Denso compressor for the OP's car is $319 and the price for a new, OEM receiver/drier (which is necessary if you open the system) is $79. It is literally
impossible for the OP to replace his compressor and receiver/drier for "under $300" (the number you threw out). He's $400 in with only the main parts. If there's a leak anywhere else or if he has to flush the system (which he should), then there's extra money on top of that. And then there's the cost of a vacuum pump (realistically the OP probably doesn't have one just sitting around).
ZV