I've been in the A&P business for over 40 years starting as an USAF Crew Chief on Jet, over 2 engines,C141, C5's, B52's and retired as USAF Reserve Flight Engineer on C141 's. Currently an A&P Inspector at Alaska Airlines on Boeing 737 aircraft, with thirty plus years heavy and line maintenance experience.
Right now is actually a very good time to get into commercial aviation, that is airlines or main line carriers (United, Delta, Alaska etc) and Regional. More money will come from the main line carriers. Currently there are are many retirements going on or projected to occur in the next five years. At my employer alone we expect in the neighborhood of 25-30 % work force retirements in those next five years. I'm one of them along with many of my contemporaries here and similarly at other carriers. An older generation of mechanics/technicians are making way for a new.
Main line carrier techs make the most money to start and there is a progression up the pay scale, sometimes up to eight to ten years to top out in pay. Most are union which for the most part is a good thing, very nice to have an actual employment contract, which is a real protection. Pay scales go down from there, regional, corporate, then general aviation and all will have a pay scale. As an aside, you can move to other airlines if you choose and it is easier if you have airline experience but, you will typically start at the bottom of the pay scale, no such thing as a journeyman like other trades. All can be very satisfying as a career.
As you may know an A&P school is usually a two year course possibly resulting in an associates degree and the opportunity to take your FAA written and oral tests to be granted your Airframe and Powerplant Airman Ratings. There are other ratings also if you choose to go into avionics. Also, there is a shortage of projected A&P's so in addition to hiring ex military, recruiting is going on at A&P schools. Some carriers actively participate in various schools knowing the have a wave of technician replacements needed. Alaska is one example.
An average top out for a main line carrier is in the 80-90K range and it goes down from there to general aviation being typically lowest and mostly working for a small shop on local airfields. Main line techs can go to almost any city where the carrier has maintenance staffing, this based on seniority as is the shift you work. Expect to be on grave shift without weekends off for a while (read that years). Most operations are 24/7, 365 days a year. There is the potential for considerably more cash depending on the overtime offered and if you accept it. Seniority typically governs the order overtime is awarded.
Many in the business start with military aviation which is good invaluable experience. Some stay for a twenty year military career and then start another career at an airline or other related career. Just saying that there are times every 20 years approximately, when there is a turnover and new staffing are hired. This is happening currently, as it was when I hired in.
For the most part I have enjoyed working on airplanes. Pretty cool to see them head to the gate on time ready for a load of passengers. As far as the cost of training I think it would be well worth it and there is an excellent chance of spending your entire career doing what you like. Good luck and hope this helps.