I took a bit to wrap up some camera buying advice and after writing it up I realized more people could possibly benefit from this so I’m going to share it here because sharing is caring.
I’ve been thinking about it and I didn’t want to give my recommendation as it’s one of the cameras I want to get next for myself but I will just let you know that up front and that should address that bias.
I would recommend a Canon 50D.
It’s a more professional level crop sensor camera with a weather sealed body and shoots 15 Megapixel stills.
Reasons I would not recommend it would be if you want a really cheap camera, these are a hair under $300 used and you can get something that gets the job done and is fun to learn with for about $100 if you just want something you can swap lenses with and get digital pictures you can print.
It has no articulating screen and you might prefer something a little more entry level like a T3i that does have an articulating screen.
It’s EF mount and all that is good and bad with that. You can use a lot of different lenses but not as many as mirrorless and it does not natively have focus peaking, although that can be added with Magic Lantern.
Now for the positives.
It takes Compact Flash so it has a lot of bandwidth for really fast communication which can be taken advantage of with stuff like Magic Lantern.
It has a bigger sensor than most anything else you could afford in this price range (Unless you want a first gen 5D)
It’s weather sealed so you don’t have to freak out if it rains.
It is beastly as a Video Camera with Magic Lantern only falling short of the 5D Mark III which is a $2,000 used camera. That said it doesn’t have a microphone but you shouldn’t use an onboard mic for video anyways.
To sum it up this is my favorite affordable used Canon DSLR and I think it’s the best option as you have more lens options than Nikon thanks to the flange distance and available adapters for Manual Focus lenses and the wide selection of EF and EF-S lenses. That said it may not be the perfect camera for you but it’s a good example of how much more camera you can get for around $300 used compared to $100 -$150. Those cheaper cameras are great to learn on but if you want something to really grow with I think taking the time to save a little more money for your initial investment will serve you better in the long run.
Good Alternatives would be:
a used Panasonic GH2 for $300.
You give up some sensor size and therefore lose some low light capability and shallow depth of field capability but you get the advantages of a mirrorless system with even more options for lenses and an articulating screen. Native Panasonic lenses will cost more than comparable Canon lenses though and there is less selection available.
Sony A5100 for $300 used.
A lot of the same benefits of the GH2 but in a very compact body. You do give up a viewfinder for that though.
All of this stated there are still a ton more options to look at that are all good recommendations but this is just a good example of how much camera you can get on the used market for $300. If you just want something to play with and learn and are not concerned about the overall quality of everything you can still get tons of different cameras for under $100 used.
Hope all this helps.