Ever since I started playing this game, I've wanted to know how much I was paying whenever I leveled up any of the idle vote options (Leaflets, Billboards, Etc). Though you only need to purchase one Leaflet to unlock Billboards, multiple Leaflet upgrades cost you less per vote-per-second than the first Billboard (8 Leaflets, in fact). This guide contains charts of just how many lower level upgrades you should purchase before buying the first of the next highest upgrade available.

Obviously, Leaflets are the first upgrade. I tend to level up my clicks as much as possible first so I dont have to spend much time actively at the game if I want to, but yes! Buy some leaflets :3

Before buying your first Billboard, you should know that a total of 8 Leaflets upgrades cost less for the votes-per-second you recieve from upgrading it than your very first Billboard upgrade. This is how the upgrades you should buy will be shown in this guide:

Leaflets | x8
Billboards | x1

saying that you should be up to your 8th upgrade on Leaflets before it is worth the cost to buy your first Billboard.

Leaflets | x27
Billboards | x11
Grassroots | x1

Leaflets | x38
Billboards | x17
Grassroots | x11
Merchandising | x1

Leaflets | x47
Billboards | x22
Grassroots | x19
Merchandising | x7
Radio Ad | x1

Leaflets | x47
Billboards | x22
Grassroots | x19
Merchandising | x7
Radio Ad | x5
Newspaper | x1

Leaflets | x52
Billboards | x25
Grassroots | x24
Merchandising | x11
Radio Ad | x5
Newspaper | x8
TV Spots | x1

Leaflets | x60
Billboards | x29
Grassroots | x30
Merchandising | x16
Radio Ad | x10
Newspaper | x13
TV Spots | x5
Autobiography | x1

Leaflets | x72
Billboards | x36
Grassroots | x41
Merchandising | x25
Radio Ad | x18
Newspaper | x22
TV Spots | x12
Autobiography | x10
Social Media | x1

Leaflets | x86
Billboards | x44
Grassroots | x54
Merchandising | x35
Radio Ad | x28
Newspaper | x32
TV Spots | x19
Autobiography | x21
Social Media | x11
Copywriters | x1

Leaflets | x86
Billboards | x44
Grassroots | x54
Merchandising | x35
Radio Ad | x28
Newspaper | x32
TV Spots | x19
Autobiography | x21
Social Media | x11
Copywriters | x7
TV Ad | x1

Leaflets | x103
Billboards | x53
Grassroots | x68
Merchandising | x46
Radio Ad | x40
Newspaper | x43
TV Spots | x28
Autobiography | x34
Social Media | x24
Copywriters | x15
TV Ad | x17
Endorsements | x1

Leaflets | x107
Billboards | x56
Grassroots | x72
Merchandising | x50
Radio Ad | x43
Newspaper | x47
TV Spots | x31
Autobiography | x38
Social Media | x28
Copywriters | x19
TV Ad | x22
Endorsements | x10
Countrywide | x1

Leaflets | x120
Billboards | x63
Grassroots | x84
Merchandising | x59
Radio Ad | x53
Newspaper | x56
TV Spots | x38
Autobiography | x48
Social Media | x38
Copywriters | x30
TV Ad | x35
Endorsements | x13
Countrywide | x12
Song Writers | x1

Leaflets | x159
Billboards | x65
Grassroots | x87
Merchandising | x60
Radio Ad | x56
Newspaper | x59
TV Spots | x41
Autobiography | x51
Social Media | x42
Copywriters | x34
TV Ad | x39
Endorsements | x16
Countrywide | x16
Song Writers | x10
Microtargetting | x1

Leaflets | x[<163 up to $100,000]
Billboards | x68
Grassroots | x93
Merchandising | x66
Radio Ad | x[<65 up to $1,000,000]
Newspaper | x63
TV Spots | x[<47 up to $8,000,000]
Autobiography | x56
Social Media | x46
Copywriters | x[<41 up to $20,000,000]
TV Ad | x45
Endorsements | x20
Countrywide | x21
Song Writers | x[<12 up to $2,000,000,000
Microtarget | x10
New Media | x1

Leaflets | x[<164 up to $162,000]
Billboards | x72
Grassroots | x99
Merchandising | x71
Radio Ad | x[<65 up to $1,620,000]
Newspaper | x68
TV Spots | x[<48 up to 12,960,000]
Autobiography | x62
Social Media | x52
Copywriters | x46
TV Ad | x52
Endorsements | x25
Countrywide | x27
Song Writers | x[<12 up to $240,052,000]
Microtarget | x10
New Media | x10
Twitter | x1

So I hope all these charts help you spend your votes wisely ^^ Once I get farther than the Twitter Strategist upgrade, I will add to this guide. I will also find the exact upgrade levels for the ones in [] brackets on my next landslide runthrough.

Have fun clicking your candidate to presidency :3