ShinHan has a line they call Professional Poster Colour. Here in Canada at least they are inexpensive (about a quarter the price of Winsor & Newton) and they feel pretty decent to me – not quite as nice as M Graham or W&N but good – definitely superior to Pebeo, the other inexpensive brand I’ve tried.
They come in 40ml jars which locally cost 8 bucks and have a large colour selection.

I have to make a plug for this jelly cup gouache from Miya. Just search “Miya gouache” on Amazon and you will find it. A set of 18 30ml cups sells for $18 USD. Other than (probably) not being lightfast, everything else compares very favorably to professional gouache (MG is my normal artist grade). Excellent opacity and pigment load, great consistency, portable box with very secure seal, really easy to work with.

The only downside is that this 18 set of 18 is the only thing you can get in the US for now. But the company in facts makes a huge color range and many different sizes, oh and they also make cheap acrylics. Here is to hoping they will eventually sell more stuff in the US. And also hoping with more sales they can bring down the price more to match their actual pricetags in China. (That $18 set is suppose to be $7, but I guess they do have to ship stuff to the Amazon warehouse. ) I know what I am loading my luggage with next time I am in China.

https://www.amazon.com/Gouache-Portable-Students-Watercolor-Painting/dp/B07D5VGGQN/ref=sr_1_1_sspa?ie=UTF8&qid=1543878615&sr=8-1-spons&keywords=miya+gouache&psc=1

Well, you asked for something cheaper that you could learn with but it seems you want Holbein quality for a cheap price and, even though it’s what we all want, it’s not available.

The Nicker poster color is certainly not cheap and is also very hard to come by at times. It’s also of questionable (for most colors) lightfastness as it’s designed for animation. I’ve wanted to try it but couldn’t bring myself to invest in something that might fade quickly.

Have you read the sticky thread on gouache comparisons? DaVinci is a decent brand that I like but, of course, I prefer the MGrahams or Schminke but I learned with the Lukas. I’ve been an artist for a very long time but I can assure you I didn’t make any masterpieces when I started with gouache! Learning with a cheaper brand just made sense at the time.

However, I believe in using the best supplies you can afford and only you can decide what you need to do. Good luck finding your balance between price and quality.

Ok, I know what I’m going to recommend will probably be seen as heretical, but I recommend Dick Blick Premium Tempera at $3.59 for an 8oz bottle ($5.10 for a 16oz bottle). I know that the color selection is slim at only 15 colors (I didn’t count any of the metallic or fluorescent colors). On the plus side the colors are creamy, matte, and rewettable.

I don’t know how lightfast the colors are, but Blick lists them as “Brilliant, Lightfast color.” Blick makes multiple temperas. The “Premium” is the top of the line (read most expensive) of the bunch. Before, I started playing with gouache I bought a bottle of white and black and then proceeded to go to town in monocolor. I then bought all the other colors they had.

I own a complete designers box set of Winsor & Newton (read the whole line of colors) along with some colors long out of production that I still use (why did they dump Cadmium Red Deep). I also have a bunch of other colors from most of the other makers. But, on my desk always at hand are my Dick Blick Premium black and white.

I am not a great artist just a retired guy who enjoys drawing and painting. Just to let you know who the recommendation is coming from.