Questions about Tires due to Dry Rot?

[explicitdwk]

I apologize in advance for i know this topic has been discussed before however i am an amateur to owning a car in general. therefore your advice is EXTREMELY appreciated!
I was in BMW of manhattan for service this past week and my SA asked if i wanted to replace all 4 tires because of dry rot and there is a fairly deep gash in one of my rear tires. I have realized the discolor of the tires these past few months but thought noting of it. I have the OEM MICHELIN Energy™ MXV4® Plus 255/55R18 105H and it is a 2006 model with 28,xxx miles on it.
BMW quoted me almost $1,500 for all 4 and an alignment

Normally i would think nothing of it and ignore the dealership offer and head to pepboys or something. however it is my first luxury vehicle so i was wondering if that would be okay? or for suggestions?
I spoke to someone at pepboys and they said they could order michelin tires for me but I'm not sure how they would be then charging me for their services.
Are there better tires preferably all seasons in the Michelin price range(or a little higher is not a problem if better)?
Are alignments normally $200 plus tax? im sure i can find it for cheaper but i wonder if BMW's quality of work may be more suitable(because they know it better?)? HELP PLEASE! thanks!