Don't fear the steam engines!
Josie, as a newbie on a budget, you have the right suspicion that steam locomotives in N-Scale could be more pricey. But, you can do it, and it you want to model the 1950s, there certainly was a lot of steam still around (unless you are talking 1958, when it was all virtually gone!).
My biggest caution would be to "BUY QUALITY". In steam, in N, if you buy cheap, it is a complete waste of money. It won't just run "so so"; it will be junk. Having said that, you can find some good-quality steam without spending brass prices.
I had HO as a kid.
When I started out in N, the first engine I bought, in 1985, was a Concor 4-6-4 Hudson. Little did I know that I luckily stumbled into buying the best N-Scale steam engine ever made (at least at that time). I still have it, and it still runs smooth as silk. It was lettered for Pennsylvania, which was bogus. But I've since relettered it for New York Central (much more appropriate for a Hudson).
These days, I would suggest the 2-8-2 Mikado made by Kato (who also made the above-named Hudson for Concor!). You can usually find these online for under $100, or at train swap meets, or on Ebay. Retail pricing on them is usually much higher, like $125 - $140. But it's not hard to find them under $100. I bought my last one at a train show for $55 (quite a deal!)
They run great right out of the box, and look as good as they run. Threre is a replacement set of driver wheels with a rubber traction tire on it. This wheelset costs about $7-8, and is well worth it. The engine can only pull 6-8 cars uphill without it, but more like 20 with it. On level track, it can do about 10 without it, 27-28 with it.
My second choice would have to be a Concor 4-6-4 Hudson. You'll find these all over the place as old as the 1970s or brand new. They made so many runs of them, I can't keep track of them. Some were made by Kato, some not. Just make sure you can test-run it if you buy it at a show or a swap meet (always do this, with ANY engine at a train show, because once you go home, you're stuck!) If you find a new one at a store, you'll be fine.
Again, the retail price is pretty high on these, but dig around. Don't pay more than $100.
Third choice would be the Bachmann/Spectrum 2-8-0 (not the plain Bachmann steam locomotives, they are absolute trash... make sure it's a "spectrum"). It should cost $60 - $80. If you are looking at an ad somewhere, and the price is like $35, forget it. It's a non-Spectrum and will lead to tears and frustration.
Other Spectrum models aren't as dependable, so stick to the 2-8-0, in my opinion.
I do have a GG-1 (the electric that some other posters recommended). This is a beautiful-looking locomotive, made by Arnold (now Rivarossi) years ago, and made for a long time. You can still find them around. But beware, these don't run very well in my opinion. I ended up putting a better-quality motor in mine, adding flywheels to the driveshafts, and adding bronze wipers to get electrical pickup from some of the wheels that didn't have pickups on them originally. If you are new to the hobby, you probably don't want to get involved in something this complicated, so I'd avoid this engine for now. They are also quite expensive, again, unless you can score one at a train show.
Speaking of trainshows, I think that you are not too far from Timonium, MD? There is a very large train show/swap meet there, 4 times a year, known as the Great Scale Model Train Show. You can look it up at
http://www.gsmts.com
They usually have 500-700 tables, all scales (not just N), but there is quite a bit of N at this show. I've gotten a lot of bargains there.
Good luck!
