I too got by with 120 volts for a while when living in a place with no 240 access. Some tips.
-Use the maximum wattage element you can without blowing the breaker
-Use a second or third outlet in your house to be able to run all elements at once, i.e. find which outlets are on different breakers, I did this with two long extension cords of the correct rating
-Consider using a HERMS system in which the pump cycles on and off to pull heat out of the HLT for the Mash tun. This allows you to heat the HLT to say, 175 F, then just recirculate mash when you need heat. Not ideal, but allows the HLT heating process to take place slowly on brew day, then the 10-15 gallons of hot water act as a battery when the mash needs heat, and the small little 120 V element can keep up with this leveled demand. You will have problems with step mashes, but a single temp mash works perfect.
It is very easy to switch to 240 later, do not let the 120V limit get you down, here is a look at my system, I recently switched from 120 to 240 V. The entire change over was about 15 minutes as i had to re wire one plug, and one controller power source. I also changed an element, but that was not necessary, just done to deliver more wattage to the HLT now that I had 240.