Hi, Havannah,
Well, you need to know that as with anything, even clothes or electronics, a cheaper stroller will mean compromising on features and comfort. So the lower you get - like with Kinderkraft or Graco models, the cheaper, more plastic the fabrics, the less soft suspension, the less comfort features and less all-terrain capability.
When going for a compromise, it is good to think about getting a stroller second-hand, too - you can go for. better, higher quality brand that is cheaper when used, though still performing better than a cheap new pram.
For bumpy roads, larger wheels and sizes are better, though for public transport, smaller wheels and frame are the better option. I cannot generalize one brand a all mentioned brands have their positives as well as negatives, and it also varies heavily with every stroller model.
If I were to get a new, reasonably affordable stroller, I would most probably think about the Joie brand as their price-performance ratio is actually one of the better ones. If you really need to save money, go for the non-reversible Joie Litetrax Air which will work ok on bumps and can take on a bassinet as well as a car seat - a complete travel system while simple enough to be affordable. The Joie Versatrax is also worth mentioning as a reversible, full-featured model with a doable price tag.
From Kindekraft, check the Evolution or the Nea for adorable pram.
From the more all terrain three-wheelers, I would go for the Baby Jogger City Mini GT2 though that is not a cheap pushchair, and you might really want to check it pre-loved. And also check the Cybex Balios S which could suit you, too.