I have a client who wants his online cigar shop redesigned. Along with
basic e-commerce functionality, we need the following:

a. extremely flexible in terms of layout (the core design for the site is here.)

b. generates search engine friendly pages

c. allows for customized SEO (header tags, alt tags, etc...)

d. supports discounts, coupons, gift certificates, etc...

e. in addition to product sales, can handle the following functionality:

a 'cigar club' where people would pay a recurring monthly fee that would
entitle them to an automatic discount on all purchases, advance access
to sales, special member-only offiers, free shipping, etc...

f. be as cost effective as possible -- not averse to using open source if it
is stable.

Any recommendations? The client is on a severe budget (can we say
tight fisted?) but it's a project I'm excited about.