If you can get a good overdriven tone from your amp, then I'd say definitely a delay pedal. If you get one with multiple settings, "echo" or "analog" usually will have the highs dampened on the repeats, which helps the repeats to blend into the background better. Use it well and it will really fill out your sound a lot.
With your amp, try turning the "gain" up on the overdrive mode and turning the "volume" down. Don't be afraid to turn the gain all the way up. This should get you an overdriven tone, but it looks like your amp probably doesn't have the controls to get balanced levels on overdriven and clean.
With the kind of budget you're on, I have another suggestion: a multifx pedal. I know some guys will chime in saying that they don't sound as good as regular stomp boxes, but a $100 mfx can get you emulations of several overdrive pedals, as well as delays and chorus and such. Mfx units also have tuners onboard. As far as bang/buck goes, it's really hard to beat a mfx, and, nowadays, the tone really isn't all that bad. As someone using a 10 watt SS amp, I doubt you'd be in a position to appreciate whatever subtle tonal advantages analog stomps may have.
I'd recommend a
Digitech RP90. It looks like a good option for around $100. It's got enough amp and stompbox models to give you some options, but not enough to bury you.
Another cool thing about a MFX pedal is it can help you get a feel for what kind of gear you need to get the sounds you're looking for. The fact is that with amps and pedals and all that, there is a HUGE amount of subjectivity in evaluating them. There isn't very much "better" or "worse," but mostly just "different." Plus, a mfx lets you try out a lot of different stuff without having to go buy more gear.
Honestly, for the amount of money it would cost to get a good OD pedal, a delay, a tuner, and maybe another pedal or two, you would have been a good ways towards getting a decent amp. If I were in your shoes, I'd pick up a mfx pedal and save money for a nicer amp. You didn't say what your church's amp is, but I'm going to guess that it's probably not all that great if it doesn't even have reverb (yes, I know there are some good amps that don't have reverb, but I doubt his church has one of them).