I think the ace 150 is an excellent choice, my family,wife and kids just got into detecting last year and we bought a used 150 as our first machine. We have a 400 now and i think the 150 has found just as much of the good stuff! The ace machines are great for coins and the smaller coil on the 150 is better in trashy areas and easier to swing. the 150 will find more hot rocks it doesnt have a learning curve though you can pretty much turn it on and go.
you'll want a good digging tool also, we have a couple shorty shovels ,one flexes alot and you have to use care not to break it, plastic handle and flimsy thin shovel head, it is fairly light weight. Our other shovel is all metal and 5x stronger its just a better tool all around and doesnt weight much more. Garage sales are a great place to find diggers