Rate for translating a kids' math board game from English to Spanish?

Hello fellow translators,

I was recently hired to translate a math game for elementary school students from English to Spanish. The company asked me to look over the game and let them know my rate. It seems like the type of project for which I would just give them a flat fee as opposed to charging by word or by hour. However, since I'm new to the industry, I'm very unsure of what to charge--I don't want to end up charging too little or, conversely, suggesting a ridiculously high fee. I know the rate might be hard to ascertain without seeing the game, but essentially I would be translating the box, one page of frequently asked questions, one page of "quick start" directions, one page detailing what comes in a deck, a four page mini pamphlet with more detailed instructions and rules, and a few words that come on the cards and the score pad (around 1900 words in total). Does anyone have any suggestions or know someone who might? I would really appreciate it! Thank you so much!

Best,
Nina