Play It Again in Dedham is pretty good and has inexpensive used equipment

Putting the same amount in every week or month is DCA. The alternative would be waiting until the market seems low, buying a bunch of stock, and then not buying any more for a long time until the market seems low again

I think DCA generally performs better / is safer. Personally, i do it - I have it set up so a portion of every paycheck is deposited into my brokerage account and invested.