You still call it Freon is a trademark name for R-12. For clarity sake, call it what it is, it is R134a.
If you don't know what you are doing, you stand to do far more damage doing it yourself. Unless you have a lot of vehicles, you will not save any money doing it yourself unless you have several vehicles. You will need as a minimum, a good vacuum pump, a good set of gauges, a good thermometer, a good book on how to service AC
systems, and misc other tools. You up front cost on tools alone is about $200 depending on the quality of the tools.
If you don't know how the system is, you can't fix it reliably. As stated above, you need to know why, how much, where, and what. If you add refrigerant, and it has a leak, it will continue leaking. If the oil escaped too, you will not have enough oil, if no oil escaped and you add some, it will be overfilled. If the system was already full, it will be overfilled. If the compressor is dying, it will die worse if you refill.
A pro can refill for cheap, and most of the time, they count the recheck in the initial price plus any charge that is lost. If you have further problems, they can help fix them.