If you already have several pairs of shorts and jerseys I'd say the cheapest option would be leg warmers OR light unpadded tights (the leg warmers do fine on me, the tights are a little sleeker but warmer), midcalf thin wool socks, arm warmers, a vest and thin fullfinger gloves. I prefer covering everything with a thin layer instead of leaving skin exposed as with knickers, but we tend to get wet weather around now.

There's a bit of difference in arm/leg warmers though - I have Assos arm warmers which are very sturdy, thick and warm (the grippers are almost annoyingly "sturdy") but Sportful leg warmers, which are very thin and breathable, and look like they might get sloppy around the knee with use.

I do the spreadsheet thing too - invaluable whenever the seasons change