If I understand you correctly, there are plenty of cheap options that are more than strong enough. The height you're talking about isn't anything major. Take a look at Josh's frogs for some options. You might want to consider a little foam box to go around it or something for added filtration, but I think you can easily achieve what you want for 20-30 dollars or less.

Speaking from experience, you'll definitely be careful with the gallons per hour. The difference between a serene water feature and an snowmelt torrent coming down from the mountains is less than you may think. As such, I'd recommend pumps under 100 GPH with an adjustable flow. I had mine dialed in on the low side and it was more than enough.

Additionally, I'm pretty sure most salamanders aren't a big fan of fast moving water anyway, so a slow flow sounds good. Maybe a series of small pools, instead of one long stream? Hopefully someone else will have specific recommendations for you. I bought mine ages ago, and no longer remember the brand.

Something to consider... I think my tiger salamander defecated on land mostly, but you might want to double check if that's the norm. It will be very hard on the pump if there's a lot of detritus floating around, so you'll either need to take some extra steps or maybe come up with a new plan. A lot of pumps have a built in filter, but that should be treated as a last line of defense.

edit: Googled out of curiosity, and yes, they do mostly defecate in water. I'm sure you already know, but they are fairly terrestrial as well. I'm not saying the water feature is necessarily a bad idea, but I just want to state the obvious and say I think it's probably less for the salamander and more for the human. There may be better ways to spend the limited space than a stream, and definitely better than my idea for a series of pools. Just something to consider. ( Does sound pretty, though. )