Shop where the machines are sold and serviced.
Take your parent with you so the clerks will know you are serious.
Tell them what you want to be able to sew. Take a piece of denim and leather with you - both need specific needles; denim and leather. A universal needle will not do a good job piercing thick material.
They should demo the machine and then let you try.
For $300 you may find a slightly used Bernina, which is the best made. Babylock, Brother, Viking, Pfaff and Janome are also great machines.
A used Bernina, in fine running shape is a better machine than any other another, new.