I would recommend getting on forums like this often, and also joining some of the facebook pinball buy, swap, sell pages as these days you need to be quick to get a decent priced pinball.
4 years or so ago 3k would have got you a nice DMD, but sadly those days are gone. They are at least 5k for a nice DMD now.
I would not limit yourself to DMD, I would also advise going to some meets if you can to meet some pinball people and play some games to get an idea what you like. Pinball is very subjective, what you love some may not like at all.
If you do not know much about pinball i would take someone who does with you to go over it to make sure it is a solid purchase, while buying a pinny can be fun it can also be costly if you let your heart rule your head.
I would advise going through some sold pinball threads on forums to get an idea on prices, but only go by the last 3 to 4 years tops! Go any further back and you will get depressed.
Hope that is helpful.
