Cheap as possible but a decent tool for the price, I'd recommend a KR808 system, a 2 piece systme (look like the regular cigarettes, mostly). If you like the gas station disposables, you will find the actual batteries much better.
Just a note, those Blu disposables are around 24mg nicotine, which was way too much for me. But, might be perfect for you.
Check out kits that give you a minimum of two batteries. One to vape, while the other charges. An additional battery for backup is a good thing to have, as well.
Kit prices vary depending upon the vendor you go to, same with quality. I have the expensive batteries, and I have really cheap batteries, and I have the "just right" batteries in the middle. As my signature might suggest, I prefer the batteries from Smokeless Image. Excellent KR808 batteries, available in lots of colors, two lengths, and two switch types - auto and manual. My first recommendation for a kit from them is the Standard, which provides two batteries, the basic charging system, and a pack of cartomizers. If you like them, then move up to a Pro kit, which offers a couple more batteries and a pcc (portable charging case). I like getting the kits, prices are usually slightly better than ala carte selecting. Once you find you like something, then move to the refilling and liquids options. I think their cartomizers are reasonable, but there are carto's available from lots of places. I like the flavors better from Smokeless Image for the pre-filled carto's.
There is a simple passthrough KR808 battery available from Smokeless Image which is not "portable" but if you get it (available in the Premium Kit or ala carte), don't plug it directly into your computer, use a separate USB hub with a 1.5A output or better, or use the 1.5A wall charger available separately and plug into the wall or a power strip. At this point, though, I think I'd recommend their new X2 battery instead of the tethered passthrough ("big" battery step up as mod/APV), as it will hold a charge for a lot longer and is portable. Although I have not given up my regular batteries from Smokeless Image, the new X2 is mighty nice to have. The regular cartomizers are usable with it, and also has a new clearomizer to hold a lot of liquid, which is also usable on the regular batteries, though it will look funny and feel a bit lopsided. Again, you can charge the X2 at the computer, but I wouldn't vape as it charges. I'd stick with charging using the 1.5A wall adapter.
There are many other choices out there. Some cheaper, many more expensive. For super cheap, You can get a $65 kit from MyVaporStore.com, which includes a pack of random carto's and the tethered passthrough, but the batteries are what you pay for. They still are a decent backup to my Smokeless Image Volts, though. I prefer Smokeless Image for the quality of their product and their great choices for accessories, and their more than excellent customer service.
There will be other opinions, but you wanted to stay on the inexpensive side, so Smokeless Image would be a good choice.
Definitely do some more reading here at ECF before making a choice. There are many different systems and things to consider. I personally don't recommend skipping the "lower" end 510's or KR808's before heading to mods/APV's, but that is my preference only. You'll find something right for you in all the information available here.
