I used a cheap brand similar to the dollar store and only cost a dollar and got a positive this month. Other months were neg. I think they work fine no matter what thecost as long as you use them according to the instuctions!
I have not used OPK's from the dollar store, but I do use the cheapest ones from CVS. The are the kind you dip into a cup that you pee in. I think they are like $17 for a tube of 20 of them (less than a dollar a test). I get my LH surge every month. Hope this helps.
I was asking about OPKs, not HTP :) thank you though!
I just bought one on Thursday = BFP. Confirmed by blood work
I figure that if I am pregnant it is going to show no matter what the price of the test is after all they are looking for the HCG hormone.
BTW I always buy them from there and I am happy with them.
Good Luck.
I have not personally used them. I know many women on here do. I think they are happy with them.