>>4440560
That depends on several factors.
1. What do you consider value? Games with the best yuri? Games with the most content/playtime?
2. What genres do you like? If you dislike VNs for example that changes the recommendations.
3. Are you from the USA? You say dollars, but every store has different prices.

40 bucks is not a lot to work with, but I will try my best.
Under the assumption that you want the most yuri value:
Please Be Happy $13.39
https://store.steampowered.com/app/844670/Please_Be_Happy/
Lilycle Rainbow Stage!!! $9.99
https://store.steampowered.com/app/978870/Lilycle_Rainbow_Stage/
Haven $9.99
https://store.steampowered.com/app/983970/Haven/
Mass Effect Legendary Edition $5.99
https://store.steampowered.com/app/1328670/Mass_Effect_Legendary_Edition/
The Fruitless Flower 雾雨中的徒花 $0.49
https://store.steampowered.com/app/766560/The_Fruitless_Flower/
Overall = $39.85

Under the assumption that you want the most playtime/content with yuri:
Volcano Princess $7.91
https://store.steampowered.com/app/1669980/Volcano_Princess/
Mass Effect Legendary Edition $5.99
https://store.steampowered.com/app/1328670/Mass_Effect_Legendary_Edition/
Fallout 4 $7.99
https://store.steampowered.com/app/377160/Fallout_4/
Pathfinder Wrath of the Righteous $6.99
https://store.steampowered.com/app/1184370/Pathfinder_Wrath_of_the_Righteous__Enhanced_Edition/
Dragon's Dogma Dark Arisen $4.79
https://store.steampowered.com/app/367500/Dragons_Dogma_Dark_Arisen/
Stardew Valley $7.49
https://store.steampowered.com/app/413150/Stardew_Valley/
Overall = $41.16
I hope diverging by 1 dollar is not a dealbreaker. It would have been cheaper outside the US.

Worth mentioning is that for most of the games in the "content" section there are plenty of mods to enhance/artificially increase the yuri and content in general even further.