This script

Sets
mp_hudscale to 1

Occupies 37 (28 while
cbm.light is set to
true) hud texts in total (the IDs between 110-147 or 110-128)

Occupies three bindings: "B", "mouse1" and "escape"
Documentation
It is not recommended to change the core script but feel free to configure it.
Light mode
Set
cbm.light to
true to activate the light mode (see feature #6).
Menu color
You can change the color of the menu:
cbm.color = {255, 255, 255}
Values go like
red,
green and
blue, as you can tell.
Menu content
If you want to change the menu content, you will change the content of the tables called
cbm[1]
(for Ts) or
cbm[2]
(for CTs).
Whilst it is really easy to get the hang of it, I will not hesitate to teach step by step.
To create a basic buy button, you just have to insert a table containing the item ID and the price to the particular table. Like this:
{1, 500}
. This is simply a new button that sells USP for 500$.
To create a submenu, you have to insert a table that contains the menu's title and its content:
{
	title = "Pistol",
	content = {{1, 50}}
}
content is actually another table that would contain items to sell or other submenus. In this case, this a submenu titled as "Pistol" that has single button which sells USP for 50$.
Make sure to not leave
content empty as it would occur errors otherwise.
Let's configure CTs' buy menu:
cbm[2] = {
	{
		title = "Weapons",
		content = {{
			title = "Shotgun",
			content = {{10, 1000}, {11, 1000}}
		}, {
			title = "Pistol",
			content = {{1, 50}, {3, 500}}
		}}
	},
	{56, 200}
}
Replace this with yours and see how it looks in game.
Warnings

Do not attempt to sell Red Flag, Blue Flag, Bomb and Planted Bomb since they are not equippable.

Make sure to not exceed more than 9 values at a table. Buy menu can accept up to merely 9 buttons.