User can specify a price that he paid for a series

[php-coder]

It should be only available after user added this series to his collection.

[0pdd]

@php-coder 4 puzzles #883, #884, #885, #886 are still not solved.

[0pdd]

@php-coder 9 puzzles #883, #885, #886, #888, #889, #890, #891, #892, #893 are still not solved; solved: #884.

[0pdd]

@php-coder 9 puzzles #883, #885, #886, #889, #890, #891, #892, #893, #894 are still not solved; solved: #884, #888.

[0pdd]

@php-coder 8 puzzles #883, #885, #886, #889, #890, #892, #893, #894 are still not solved; solved: #884, #888, #891.

[0pdd]

@php-coder 7 puzzles #883, #885, #886, #889, #892, #893, #894 are still not solved; solved: #884, #888, #890, #891.

[0pdd]

@php-coder 7 puzzles #883, #885, #886, #888, #889, #892, #893 are still not solved; solved: #884, #890, #891, #894.

[0pdd]

@php-coder 7 puzzles #1024, #883, #885, #886, #888, #889, #893 are still not solved; solved: #884, #890, #891, #892, #894.

[0pdd]

@php-coder 6 puzzles #1024, #883, #885, #886, #888, #893 are still not solved; solved: #884, #889, #890, #891, #892, #894.

[0pdd]

@php-coder 5 puzzles #1024, #883, #885, #886, #888 are still not solved; solved: #884, #889, #890, #891, #892, #893, #894.