Im not sure how accurate these are but at local garden stores they sell "rapitest" or something close to that. Then you put some soil from pot into a bowl and distilled water and let it set. Then you stick it inside this little container with some of the soil ph powder and let it settle. It shows you where your soil is at. I did this test and also had a soil ph meter and they both read exact same so I imagine its really close. I think those test kits are $5 or if you buy the kit it has a test for N,P,K,and soil PH for like $15
Good luck