Yes, spears weren't the cheapest of weapons, but javelins require much less wood and metal, so they should be cheaper than spears. Fom: https://www.researchgate.net/publication/291766619_Late_Bronze_and_Early_Iron_Age_bronze_spear-_and_javelinheads_in_Bulgaria_in_the_context_of_Southeastern_Europe "The way to distinguish javelinheads from spearheads is to take in consideration the size and the weight of the ends. The first type weighs less than 150 g and is between 6 and 15 cm in length. The second kind has weight between 300–500 g and length between 20 and 50 cm."
And while making a good atlatl requires some skill and work, it doesn't require weeks of whittling. I don't think that one stick should be equivalent to what a cottar makes in a season.
RQG arrows seem to cost about 0.2L, so a sheaf of 24 arrows without a quiver would be 4.8L. This is relatively more expensive compared to the Medieval prices, but bronze in RQG is more expensive than iron was in the Middle Ages, so I think that it looks about right. I've used the same system that's in RQG, ie. the players have to keep a tally of the arrows, but buying new ones is included in the living expenses (along with new scales for scale armour, sword sharpening etc.)