The next installments have pension built in. Your sim can retire and get some money every few days.
Is there any kind of mod that would allow a 'check' to be mailed like a bill, but I get money instead?
I know, I could use cheats but I'd lobe an in-game mechanic if possible.

Hi!

Don't know if it may be of use to you, but you can, kinda, simulate a pension sitation with the Payment System from Inge Jones' Simlogical, available in this link: http://www.simlogical.com/sl/downloadpages/payments.htm. With it, you can make sims write cheques or invoices of a determinate amount of Simoleons. So, you can simulate pension giving with a "Bank" household that writes this cheques and gives it to the sims, or that receives invoices from other families. You could even build a bank!

It's a pretty rudimentary way of doing it, but it's similar to your idea. Jst write down what the pension of the sim in question may be, and do the operation. Some people have created a finances system in TS2 with similar mods; with this one, that can be perfectly doable in TS1: sims could pay the bank family in exchange for a pension once they retire.