K.B.
Lantus is expensive compared to other types of insulin, but it often ends up being the most effective, sometimes only needing 1 injection per day instead of 2...you can talk to your vet about cheaper insulin, but if it ends up not working as well, or you need to give more of it, it may not be worth it or save you as much money as you think. We tend to have the best chance of success if cats are fed a high-protein diet (all canned, with no grains or starches, if possible) plus Lantus, and then sometimes the amount of insulin needed can be reduced, or even not given at all. Some cats can be put into "remission" and may (at least temporarily) not be diabetic and not need insulin.
$90 or $152 may seem like a lot, but that's over 2 months - figure $ 1.50 to $2.50 per day. Also keep in mind that until they are well "regulated", Kitty will need to be going back to the vet for follow-up visits, blood and urine tests, etc. If costs are a concern, look into applying for Care Credit - it can be used for veterinary, as well as other medical expenses, and may help with spreading the cost out and making it more affordable. Budget accordingly. Also, sometimes other pharmacies have cheaper prices - i.e. Costco.