Unless you find some incredibly sweet used deals, it will absolutely cost far more than $150.
*edit* To be more specific, if you were to buy 4 15lb bags of flourite (which is maybe a high-middle shelf substrate), it'd be $80. A "good" new canister filter would run $125-175 for that size, and a heater is $25-30. If you're really careful and search for good used deals, you can definitely reduce that substantially, but if you've found a 36g kit for $150 that has everything you want, I'd say go for it
*edit* To be more specific, if you were to buy 4 15lb bags of flourite (which is maybe a high-middle shelf substrate), it'd be $80. A "good" new canister filter would run $125-175 for that size, and a heater is $25-30. If you're really careful and search for good used deals, you can definitely reduce that substantially, but if you've found a 36g kit for $150 that has everything you want, I'd say go for it