As has been stated by Ludia staff, Speed boosts are NOT meant to be availble for purchase, as you see if you go to the store there is only health and damage boosts.
However, if you get a dinosaur to speed boost rank 3, and dont have enough speed boost points, if you click the button to apply a boost, you will be prompted with a popup asking you if you wish to purchase a speed boost for 500 dino cash!
So if you have been seeing massively speed boosted dinosaurs, when they shouldnt be able to get to that tier with just daily incubator speed boost tokens, now you know!
But please as always DO NOT use this, it is an exploit and exploiting is considered cheating!
And to remind you again, they are NOT meant to be available yet! So this IS a bug!
Dont risk your account, dont use it as tempting as it may be!
Edit: And here is the Mod post stating that Speed Boosts arent meant to be purchasable yet!