I believe that it is worth investing in maternity jeans early on in your pregnancy - they are so much more comfortable on your expanding waist, even with a small bump so why wait? Also compared to normal jeans they will have limited wear (although I have friends who still wear theirs for a Sunday roast). You will most probably be wearing them for a while once the baby has arrived too - so get some you love.
Ok so I HATE maternity clothes... or I should say hated... I bought my first pair of maternity jeans yesterday from primark of all places and I am literally in love! They are still nice and skinny and fitted but so comfy around my bump - check out my maternity video on what I purchased here; https://www.youtube.com/watch?v=r3bLjGSHMZE&index=3&list=UU-DxGKz7B0xh_zSDzgnL2cw