I'm fairly new to painting, but like you, didn't want to invest too much, at least until I "got the hang of it". Here's what I've learned so far: it's true what they say - buy the best you can afford. At the start I bought a few different brands, types, sizes and shapes, also a couple of multi-brush packages, which was a bit of a waste of money - poor quality and didn't use half of them - but what I did discover is that I tend to favour certain shapes and sizes and use them more than anything else, so in that regard, cheap was the way to go. It helped me to decide exactly what shape and size I wanted when I decided to take the plunge and invest in a few good quality brushes. I bought Winsor and Newton "Monarch" synthetic Mongoose hair and I love them. Also, I found that brushes that say they are good for oil and acrylic were too soft for oil. Found hog bristle better for oils. Again, Winsor and Newton.
For shapes and sizes, for me, a couple of scrip liners in 1 and 2, a couple of rounds, 1, 2 or 3, and filberts and flats or brights in 1/4", 1/2" and 1". These were enough to take care of what I was doing at the start, with one or two larger flats to cover large areas of the canvas. I even have a couple of 2" good quality brushes from the hardware store for that. Having said all that, there are far more knowledgeable and experienced artists on this forum than I, but this was my experience. Hope this helps.