You should ask your local pharmacist or discuss it with your doctor.
Vyvanase is still under patent so you'll be restricted to buying brand-name only. Generic time released amphetamines (e.g. Adderall) will almost assuredly be cheaper. Given that vyvanase is a chemically time released version of amphetamine, it should work the same as normal XR amphetamine salts. The one thing to keep in mind is some people are susceptible to nocebo effects induced by switching between different brands of generics (e.g. if you get the attitude that only XYZ brand will work for you, and take ABC brand instead, some people claim to get wildly different effects even though the same amount of drug is being delivered). So whatever you choose, just stick to it and try not to substitute.