A standard tuning string gauge

as far as i know, rule of thumb is one gage up for every whole step down.

 

If you have a preferred 5-string set for standard (BEADG) tuning, add .005 to the gauges of that set and give it a go.

 

This won't result in equivalent tension, only for the G string.
Roughly, for 2 semitones down, the necessary gauge increase varies from .015 for B to .005 for G.

Most brands use of gauge steps of .005 is contrary to logic and physics. Gauge steps should ideally decrease smoothly for smaller gauges (only Kalium Strings do this).
.005 is a huge (far too big) change for a .045 G but a small change for a .130 B.

The more accurate rough rule derived from physics is multiply gauge by the frequency multiplier, which for 2 semitones is 2 ^ (2 / 12) = 1.122.
For example:
.130 * 1.122 = .146
.100 * 1.122 = .112
...
.045 * 1.122 = .051

What brand/string line and gauges do you like for BEADG?
If D'Addario, GHS or Kalium use their tension charts / calculators to match to the tensions you like.

 

maybe to add to this do you know companies that sell 5 string sets closer to those gauges above that are cheaper than $30?

 

Very few of the larger companies sell pre-packaged sets with a .145 because demand is too low.
You can buy singles, or, buy a heavy 4 string set plus a single .145, or, buy from a mail order company that has no pre-packaged sets and puts sets together to order from singles (like Kalium).

 

a .145 is very uncommon i understand what about .135?

 

There are some heavy 5 string sets with .135, but they tend to be very top-heavy with excessively and unnecessarily high tension on the higher strings.

 

I think I'll stick with the .65 .45 for tuning down to A