i got a really good one from a nail technician. im sorry i cant remember what it was called. you had to paint it on once a day, two coats, then take it off at the end of the week and start again.
it was about £5 a bottle but well worth paying the extra. 3 years later and my nails are still as strong. i used it for about 6 months in total, i wanted lovely nails for my wedding, in the 6 months i had it and used it i didnt even use a quater of a bottle and was able to give it to someone else then.
i would definately recommend getting a professional one, well worth the extra money.