$1.00 pregnancy test accurate??

Berenice
Are $1.00 Pregnancy test accurate? Two of my friends once told me, $1.00 pregnancy test are as good as $18.00 dollars ones, anyways my last Period was March 28,I took a test couple weeks ago and was negative, now I'm wondering,It's time to buy a better brand.
P.S I have a son already, and my period has always been irregular since day one.