All great advice above Drew and congrats on taking steps to acquire your first machine; very exciting
Rather than posting your budget, have a machines which have sold on here in the for sale thread; that'll give you a bit of an idea of what's in your budget. Defo go to Pinball Rebublic if you can get there and play as many machines as you can; more than likely a few will really jump out to you as games you love.
Buying from a forum member here (especially if they are well known) you should be able to get something you are after at a good price and something well looked after.
It's always good if you can to go and have a look/play a machine before buying and look at for things which might need work; a seller might not know the machine they have too well and that certain things aren't working (say a bulb or flasher is out here or there, or potentially something more significant) - defo worth playing (or watching on youtube) a good example of that machine so you know how it should play and how the mechs etc should be behaving.
In case it helps, here (in my honest opinion and to my knowledge price wise) are some of the more affordable machines which come to mind which are great:
The Shadow
Judge Dredd
The Getaway
No Fear (recently started really enjoying this game at PBR and to my knowledge quite an affordable game)
Fish Tales
Road Show
Batman: The Dark Knight (might fit in to the below catergory price wise, depending what comes up - a good deal on a Transformers came up recently)
Above that price wise, you might be able to find some of the more modern Stern PROs which are great bang for your buck such as The Walking Dead and ACDC. A nice Twilight Zone sold on here for a great price recently too - life's like a box of chocolates etc, etc....;-)