All packages leaving the USA (and most going to military addresses) need a customs form.
If you are not printing the customs form from an online interface, you will need fill one out by hand, then to take your package to the PO and wait while the clerk inputs all the data on the form.
If you print them from home using an online interface (like using Etsy labels or USPS.com's label service), the data will already be sent electronically when you make the label so you can just drop the package in a mail box if you want to.
You can get cheap printers--less than $50. For example:
http://www.staples.com/All-in-One-Printers/cat_CL161518?fids=&sr=true&sby=1&min=&max=or occasionally some good deals here:
http://www.staples.com/deals/Staples-Daily-Deals/BI1142421?icid=HP:HPDEALSDROP::DAILYDEALS:20160112#...And if you sign up for their free rewards program, shipping is free. Ink cartridges for cheap printers can be an issue--they make their money there--but you can either buy refill-it-yourself kits or get them refilled any number of places pretty cheap. (You can spend twice as much on the printer--or less--and get a printer with good priced ink too if you prefer.)
If your shop sells enough, you'll help pay for the printer just by getting discounted postage printing your shipping labels online. We get commercial based pricing with Etsy & Paypal shipping labels:
http://pe.usps.com/text/dmm300/notice123.htmCompare the commercial rates to the retail rates. :)
The printer will be handy at tax time too when you need to print out documents to support your income reporting for your small business.
