I bought mat jeans early on & they lasted me right through til I gave birth. I did it as soon as my normal jeans felt uncomfy.

You don't have to spend much. I got a great denim pair from Big W for around $30 & a black pair from Kmart for around $40. Super comfy & as long as your top covers the waistband no one would know they are maternity. You will also get wear out of them after the pregnancy too - you just pull the band up higher not under the belly like you do as you get advanced.