Hot Air Popper
The cheapest and simplest is to use a (cheap) electric hot air popper. The old favorite is the West Bend Poppery, but you can use anything as long as the vent holes (where the hot air comes in) are on the sides rather than the bottom.
I've roasted a lot of coffee this way. It works, but there are a few downsides. The biggest problems:
- The circuation is designed for popcorn, which expands a lot more than roasted coffee beans. I've needed to stir the beans manually in order to get an even roast. They don't have to be stirred constantly, but you can't just drop the beans in and walk away.
- The capacity is pretty low, especially when you take the circulation into account. I can only roast a half a cup at a time, which is pretty slow.
- The temperature doesn't get quite high enough to really bring the flavors out. The roast is good, but it's really mellow.
[source: Chris g Collision, Flickr Creative Commons]
I've read about modifications you can make that will improve these: changing out resistors, modifying the airflow, and even hooking up an Arduino to control the heat a lot more closely, but it seems like more work than I've wanted to invest in the process.
Heat gun / metal dog bowl method
My brother's moved on to this approach, and I'm soon to follow. The benefit of a heat gun is that the temperature is high enough to get a good roast, and the airflow is high enough that you can roast a few cups of coffee at a time.
[source: Ocell, Flickr Creative Commons]
More Insanity
Sweet Maria's sells green coffee beans, and lists a huge amount of home roasting methods, including Weber Kettle conversions. The sky's the limit, but I'd start small with the air popper or the heat gun first.
I'd do this outside
Some methods have you roasting the coffee in your kitchen - in the oven, on the stove, etc. I wouldn't want to do this myself, for two reasons. The beans have thin husks on them, which come off as the beans are roasted. They're messy, and I wouldn't want them flying around my kitchen. Also, roasting coffee doesn't smell as good as you'd think it would.
Sources of more info:
It IS the roast that is the difference. The only real difference in the beans is that some beans taste better at a higher roast than others, so they are more appropriate for espresso. Your Italian grocery coffee company may be using the espresso label for marketing purposes, but in general, espresso coffee beans can be the same beans that are used for "regular" coffee, but roasted to a French or Italian roast level, which is darker than City or Full City.
Since the advent of Starbucks, many roasts are much darker than they used to be. Dunkin' Donuts coffee, which is a Full City roast, used to be the norm, but now a French seems to be what you can buy.
I roast my own coffee and take it to just into the second crack which is, generally, a Full City roast...a point where the character of the coffee predominates rather than the flavor of the roast. There is more information about roasts at Sweet Marias where I buy my green beans, and reading through the site will give you way more of a coffee education than you probably ever wanted.
So, yes, you can use the coffee you have to make brewed coffee. It will probably be roastier than you would normally have, unless it is just a marketing ploy, in which case it will taste normal. Consider how long you have had this coffee; if it has been shelved for a while "normal" probably won't be all that great, since freshly roasted coffee is, generally, way better than old coffee. But as long as the oils aren't rancid, it is more likely just going to be bland.
Best Answer
Domestic coffee roasters are usually 'fluid-bed', barrel or 'stirrer' type.
Upgrading from a popper to another fluid bed usually just buys you some convenience and increased roasting capacity. That being said, I had an iRoast 2 fluid-bed and that lasted at least 2 years. It was still functioning when I upgraded so it probably still works. So it may also be overall cheaper.
IMO, it's more worthwhile to upgrade to a barrel or stirrer type like the Behmor or the iCoffee. They take longer to roast, but you can achieve much better roasts and they have more capacity than fluid-beds.
Edit: Differences between roasters
Just a note between the differences in roasters.
Fluid-beds tend to roast very quickly. 10-15 mins total roast time. But this means that the outside of the bean roasts first and the inside is often lighter. The result is often a bit more acidic or 'bright'. The forced air however, does disperse smoke very quickly and it's a bit cleaner. It still has the capacity to set off your fire alarm.
More traditional designs tend to have longer roast times. I clock about 28 minutes. The slower process gives you a bean that has the same colour inside and out. Anecdotally, I would say most people prefer this. Many of the barrel type also produce a lot of smoke and not suitable for indoor roasting. However, the models I mentioned - the Behmor and the iCoffee - have after burners. This means they actively vent the smoke through a stage that burns up the access smoke and are suitable for indoor roasting.