Mostly free advertising or pay-per-performance:
Community Building (Blogging, forum active in similar themed forums, getting dugg and discussed about)
Article Submission (submit articles about phones and accessories to free article submission sites and sites that are themed for what you are selling.)
Referal Program/Affiliate Program
You said $100 to $300 ... didn't know if that was a one time deal or a monthly deal:
PPC (Google Adsense, Yahoo Publisher Network, etc...)
PR Development Campaign (Paying for links on high PR websites similar to yours, however. If you do this then make sure words like partners, sponsors, affiliates, etc are not surrounding your link and that there are no more than 20 to 30 links on a given page ... inbound and outbound.)
There are many ways of promoting ... just need to do some researching and choose the best for you. Hope this helps open some ideas for you.
Joshua C.