I've been using strimmers in my gardening work for years and a general rule of thumb is use the correct power for the job and you get what you pay for. Line strimmers are best for grass, brush cutters for brambles, scrub and even small saplings. Small electric strimmers are ok for small areas of reasonably short grass but if it's long and tough (old grass) you really need a petrol strimmer. The usual suspects for an electric one, shopping around really does pay and don't ignore the option of second hand. For petrol I have two Stihl 145, one with a string head one with polycut brush cutting blades. Stihls are pricy but really good, there are others available as they say including Echo.
I think in your situation you should either hire or buy second hand and then dump it. If it is only for a year then consider how many times you need to use it, grass doesn't usually grow much when it's cold and when it's dry.
There is a third option, if you are only going to cut maybe once or twice pay a local gardener to do it.
Finally a word of warning, strimmers can be DANGEROUS, especially powerful petrol ones. Do not wear soft footwear, users have lost toes! This is not the usual H&S ***. Also if you are strimming close to windows, greenhouses, cars, etc. do cover them with sheets or similar. Strimmers have a habit of finding small stones and turning them into speeding bullets. It's too late when you are looking at a smashed picture window! Apologies for the heavy warnings but someone should say it. Best wishes.