I started to suggest a 5-string viola, but a little research showed there's a lot of compromises with those, and you might not get a sound you like. (They're also harder to play in a couple of areas.)

I'd say that damfino's suggest of renting one or both is a good one. At least where I live (Dallas, Tx), you can rent a violin for $20/month.  At most, a viola would be $25.

Since you haven't bought one yet, I'll briefly describe my process so far, because I was where you are about 3 months ago (minus the benefit of a forum like this).

Did a lot of research, got what I thought was a decent beginner violin (Stentor 1542) at a good price on Amazon (about $250). I've since found out that brand and model isn't what I thought it would be, but it's about as good as that price dictated. I'm not knocking the brand, or saying I got a lemon.

Time goes by. I notice a number of things that just seem wrong, and in particular, the E (the highest-pitched string) sounds horribly shrill.

I work nights, so it was some time before I could talk to a luthier. I found out that factory-made violins (which is nearly all beginner ones) have a number of things done to them that are mainly aimed at preventing violins coming back to the factory. One such thing on mine was that the fingerboard was scooped much more than it should have been (to prevent buzzing). That resulted in several other problems. None made the violin unplayable, it just made it much harder to do certain things well. Price tag to fix everything up: $320.

So, be wary of buying violins "from the factory". Fiddlerman does what's called "set up" on all the violins (and violas) he sells, from what I've seen. That's worth more than you might think. (Whether he addresses issues like too-heavily scooped out fingerboards is unknown to me. I'll let him address that. I don't have any instruments from him, so I can't comment. From other people's comments, he apparently gives good value for the money, though.)

I got a violin rather than viola mainly because of money. I was impatient to get something, and I couldn't afford the extra $200-$300 that a viola would run without waiting a couple more months.  I also didn't care for the "oom-pa" parts that a viola is usually relegated to. I also wasn't eager to learn alto clef. While extremely rusty, I know treble clef.

However, if you're going to be playing just for yourself, there's not reason you can't treat the 4 strings of a viola as if they were the 4 strings of a violin, and play it just like a violin.  It would be a fifth low, but if you're playing by yourself, that shouldn't be a major issue.  (Warning - it will give you grief in lots of little ways, like trying to play along with a video, but if you don't mind it sounding like you're playing in harmony, rather than matching, it should be bearable.)

Hope this helps

Charles