Cat is trying to poop but with no success

Taking him to the vet in the morning he’s drinking peeing normaly his appetite seems a bit less frequent and he doesn’t care for treats or wet food normaly Altho did get him to eat some with some kibble today again peeing normaly he isn’t throwing up or crying when trying to go just simply nothing comes out I see a lot of times people take there cats in for this issue and get told there just constipated and after spending almost 800 900 dollars get given a laxative but he is acting normaly cuddly his normal self I know he’s feeding off my stress but is def trying to go but can’t keeps going in and leaving after no avail how much is this going to cost me can I ask for a laxative to start ? I’m going to have to go off of care credit wich I only have 1000 on and trying not to freak out as I need help with my bills after having to switch jobs :/ any help would be appreciated as I’m trying not to over think or under think it just afraid of the costs and not having enough