You guys crack me up
. EGS gave good advice, but let me expound on it a bit.
1-What makes a "pro" monitor? This is tough to quantify, but maybe the better answer is what DOESN'T make a "pro" monitor: Marketing hype and the average GC salesperson does NOT make a "pro" monitor(or headphone). A better source of advice(besides the pros here
) is to get reviews(and not just 1 or 2) on what you are considering. 2 sources I like are SOS magazine and sweetwater.com. I'm not singling out GC, it could be any music store you can name.
2-Even the absolute finest monitors on the planet can(and will) sound like crap in a bad room(as I learned from experience
). Speaker "correction" solutions can help, but will not work miracles, so if the room sucks, the software can make it suck less, but will never make it great.
3-try to do a least SOME treatment of the room. eBay sellers have rigid rockwool panels(2' x 4'). Get the 2" thick panels, wrap in burlap type fabric(frames out of 1" x 3" lumber give you something to staple the fabric to). Stack 2 diagonally across the corners and hang 1 on each side where a mirror would allow you to see your speakers(a reflection point). If budget allows, hang more on the wall behind you, and depending on the width of the room, hang a panel behind each speaker(especially for rear-ported speakers)
Here are some suggestions for better stuff(based on my experience, only):
Headphones(no order of pref):
AT Mx50
Sennheiser HD280 or 380
Shure 840(or better)
Speakers(no order of pref):
JBL LSR306 Mk II(best budget monitors IMHO)
Adam A7x
Presonus Eris 7
Adding a speaker switcher so you can AB between your Mackies and some "better" speakers can't hurt. As for testing in the car; absolutely a great idea, but do also listen to a couple of commercial releases to make sure those sound good too