All of the suggestions provided so far are excellent.
It's important to realize the economics of this new hobby that you are enjoying. The single best aspect of this hobby is that games can be a renewable resource for future games. Until this hobby goes bust, you'll always be able to get some money for a working game. The amount of money depends on a lot of factors.
This incredible aspect allows you to take calculated gambles with machines.
So if you are interested in a particular game and you can find it locally for sale, I would advise you to go ahead and buy it. Just be sure to do your homework before you pay a single dollar to the seller.
Do your own research on the game.
#1 Visit eBay and look up past COMPLETED listings for the game title in question. You want to see the price actually paid for a game. Make a mental note of the price range.
#2. Visit www.bostonpinball.biz and click on the link for "Ebay Sales Summary". Find your game and see the price listed in the "Average Most Recent 12 months" column. Then look at the adjacent column, "Count Most Recent 12 Months". These two pieces of data will give you a good starting point on the current market for the game you want.
#3. Visit www.mrpinball.com and look up the asking prices for your desired game in the classified ads. Use the search function to filter down to your game and then take a mental note of the price range.
#4. Visit the marketplace on Pinside and look up the asking prices for your game. Take a mental note of the price range.
These four steps will provide you with a solid foundation that will serve you well in your hunt for the game. Now that you have an idea about price range, you can make a calculated gamble and buy a game that piques your interest.
For example, you noted that you are interested in Twilight Zone.
Steps #1 & #2 will demonstrate that TZ has a sales average of $5,915 over 36 completed sales on eBay over the past 12 months.
Step #3 will reinforce the price range from eBay as well as introduce you games that are more expensive. As of 6/25/2014, there are 12 listings for TZ. Some are from 2013. Others are from 2014. You will see some as high as $8,000 and others as low as $5,000.
Step #4 found four listings for TZ on Pinside Marketplace. The prices found are $4,900, $5,200, $5,500 and $6,500.
So what have these 4 steps established?
In the case of TZ, you have established that $4,500 is a great deal while anything in the $5,000-$6,000 is market. Anything above $6,000 is rare and should be near perfect for you to consider buying it.
So now you know that you can "gamble" $5,000 - $6,000 on a TZ. After playing the game for 6 months, you will be able to make a decision on TZ's long term future with you. If you do not like it, you have a good chance of getting back most, if not all of your original price.
REMEMBER THAT THIS IS A HOBBY!!!
Let's say that you have to sell it for less than your original purchase price. That is not the end of the world. You are still going to get anywhere from 80%-99% of your money back provided that you purchased within the market value of TZ.
So if you buy a TZ for $5,500 and play it for 6 months and decide TZ needs to go, you have an opportunity to get back somewhere in the neighborhood of $4,500 - $6,000. Let's say you sell it for $5,140. By the numbers, you lost $360. But that $360 is not really lost money. You had a classic game for 6 months and you paid $60 a month for the privilege of playing it. That's $2 a day for a TZ.
That's a very good use of your entertainment dollar. Plus you now have $5,140 to put back into your pinball hobby.
As long as you remember that this is a hobby and that you will be spending money on it, you can experience many different games.
Welcome to our great hobby and I hope you are able to use your $19,000 to its full potential!!
Marcus