Quoted from poppapin:
Lots of places relatively nearby with all kinds of pins.
EM's your thing? There's the Village Arcade in St. Peters.
New & old there's The Pinball Gallery in Malvern & Railroad Tavern in Linfield.
These are just a few to wet your appetite.
Good Luck & welcome
+1 for the Pinball Gallery in Malvern (I'm not affiliated with them, just a fan) . It's about an hour away from you, but they have about 70 or so pins spanning every decade from the 70s to today. (maybe a couple even older that that). On top of that, their rates are ridiculously reasonable, unlimited free play on all machines (except for their 3 newest ones). $5 an hour from 11:30-1:30 on weekdays and $20 for all-day play every day they are open (or 15 bucks per person if you have 3 or more for the family rate). They post their current game list on their website. Some of the suggestions people have made are on location right now there.
The reason I bring this up is simple: while there are a lot of good starter pin suggestions here, in reality, nothing is going to beat finding a pin within your budget that you have actually played and KNOW you enjoy and don't feel you'll get bored with. Best way to do that is by finding a place with a lot of Pins and trying them all out for yourself. You'll quickly get a feel for what you like and what you don't, which will help you immensely with your first-pin search. Doing this helped me to hone in on a true wish-list and crossed. off a LOT of machines I thought I'd like but ended up really enjoying for any number of reasons.
Other than that, my most basic advice on getting a starter pin (without naming games themselves) is to look for one that had a high number of machines produced. This generally helps keep the price down (since they aren't "rare"), provides a larger base of people that can help you with advice or provide insight for any questions/issues you may have (and a lot of posts already that solve issues you may run into), and generally means that parts will be much easier to find (and trust me, you'll need parts at some point). Secondarily, look up your game on ipdb.org and make sure to download the manual, if the game you buy doesn't come with it. They have a ton of info as well as part numbers and major component/assembly diagrams you will need to get and keep your machine working great. A poorly working/maintained machine is the quickest way to people (your son included) losing interest in playing it.
T2 was my first pin. I got it for cheap in really poor condition, but thanks to its massive release numbers, with a little time, I was able to get it working perfectly. It still gets play daily.