Monoprice 1x10 Guitar Combo Amplifier - Black 40-Watt, Spring Reverb, 10-Inch 4-Ohm Speaker, High & Low Inputs, Headphone Output - Stage Right Series

A used amp would be a good idea, but if you can't find a suitable one and decide to go for something new, you might consider this Monoprice amplifier. It's about the same price as an inexpensive small practice amp, but at 40W and with a 10" speaker, it's a little bigger and louder. It also has an external speaker jack. For a guitar, it's hard to go wrong with a Squier HSS Stratocaster