Yes You can. R134a is an HFC refrigerant, or HydroFluoroCarbon. These refrigerants are not harmful to the Ozone as the CFC's (Chlorofluorocarbon) and HCFC's were, however they are still a greenhouse gas. Without getting into politics and other bs, this is the EPA stance.
I say this because that is the reason vehicles were changed to 134a. So that in an accident, the vented refrigerant to the atmosphere is OK. Also the volume of refrigerant is very small. Additionally, this is why 134a is for sale at Walmart and anyone can purchase it, without a certification.
(if your ever constipated, Google and read about the Montreal protocol. This why your home systems are being changed from an HCFC (R22) to a HFC (R410a).
This can be interpreted to mean that venting 134a with the "atmospheric recovery" method that you previously mentioned is not against the law. I could debate that it is not responsible (and that I would not make a practice of exposing myself to the vapor), but it is not illegal.
The cost of a refrigerant recovery machine is based on the fact that you are supposed to be certified and licensed to buy one. There are people and ways to get one without, but the pricing is based on the intended limited market. The recovery machine allows a person to recover and capture the refrigerant into an approved vessel/tank.
Either by using the "atmospheric recovery" method or a recovery machine, you will achieve the same result of "no refrigerant gas" in your system. There will be residual oil left, but no refrigerant.
FYI: this oil and its type is one of the major limits to changing refrigerant types in a system.
The important part to the process is the ability to pull a vacuum in your system, before you recharge it with refrigerant (either new refrigerant or the refrigerant you recovered if you had a recovery machine). The vacuum is a vital process that removes contaminants and moisture from your system.
There are "shade-tree" shortcuts that will get you cold air, but short of a good vacuum prior to charging a leak free system, more problems are inevitable.