I've come up with three options.
Most expensive first - 4* Regina Gran - still a 10-15min walk to Port Aventura but a really nice hotel. £119 room only, £132 b&b, £146 half board (not bad considering 5 evening meals each) - all booked with Hotelopia, using 9363 as discount code
4* Salou Park - £96 room only no balcony though, through Hotelopia using same discount code as above.
or go cheap as chips and treat yourself to cabs to Port Avenura by staying at the 3* Sun Club. Its is Cap Salou so a decent walk or a cab/bus ride into town, but £62 for a one bedroom apartment for five nights. For an apartment I don't think thats bad value. Thats with Hotelopia again using the 9363 discount code - which I am amazed still works after all this time!
Hope this is useful